Monday I mentioned that Tenkar's post had pre-empted one I've been tinking around with. Here is is - another consequence of perceived lethality.
GURPS combat is potential lethal. As a friend would say, "In GURPS, a kid with a pointed stick can kill you." It's unlikely, but possible. There is almost no such thing as a safe fight.
But with GURPS - probably with any character-building system instead of character-rolling system - you can make choices that improve your survivability.
You can get into what I think of as the Invulnerability Trap. That is, trying to make your defenses, armor, and death checks perfect.
Airtight Defenses: This manifests itself as the "16+ even under bad circumstances" approach to defenses. The true munchkins want Dodge at that level, because barring optional rules it doesn't decrement from multiple uses.
Why it is a trap - it's expensive to do, it's not foolproof (rear attacks, surprise attacks, multi-hex attacks, and the inevitable 17s and 18s you'll roll.) It puts you in the trap of thinking you can defend against anything you face except critical hits . . . which I've found makes people focus a potentially paralyzing amount of concern on critical hits.
Ironically, it also means your maximized defenses means it is foolish to attack with something you can defend against. Unless your GM has totally set up the entire world and then backs off forever, you can expect that high-powered challenges won't be things you can trivially Parry or Block or Dodge.
On top of that, the temptation to run into near-certain peril is strong - hey, I rarely fail to Parry, so I can take on this bunch of guys all at once! I can win this unwinnable fight as long as they don't roll any 3s or 4s!
The counter-argument to this is the "what about that time I was mobbed by (whatevers) and I had a -alot cumulative penalty to defenses?" argument. Which is fair . . . but its an example of putting yourself into a bad spot and then saying, look at how bad this spot is!
Immunity or near-immunity to death: This shows up as HT 14-16, Fit, and usually of Hard to Kill, too, if possible. Basically, no rest until your death check is 16+.
Why it is a trap - it's already hard to die in GURPS. A solid HT is worth it, so are Hard to Kill, Hard to Subdue, and Fit or Very Fit. It's just the fear of a failed death check (that is, even suffering a Mortal Wound) is so high you end up putting more points here than you need. It can pay off when there is no one to stabilize your wound.
Never Unconscious: - A related trap is the "never unconscious till I die" approach of HT, Fit, and Hard to Subdue. That one is oddly suicidal - if you (almost) never pass out, your opponents don't stop attacking you until you drop . . . automatically, at -5xHP.
Why it is a trap - Basically, because you are spending points to stay conscious in a fight that is going badly . . . and to stay functional in a fight that is going badly. It's a double-edged sword. A merciful foe might spare you if you pass out . . . but even a merciful foe is going to keep hitting you if you are half-dead on your feet but swinging for his neck. It's "I stay up until I die." That ends with death . . . and it costs you points to get this "benefit."
Sky-high Resistance: - This one is a little less of a trap. It's generally a good idea in a game with supernatural powers to have a high Will, solid HT, and some kind of bonuses against the roll. But it's not terribly cheap to have a high Will, high HT, lots of special bonuses (Resistant to, etc.) all at once.
Why it is a trap - For resistance to offensive powers, the Rule of 16 means going past a total 16 is generally not worthwhile for the victim. And while horribly virulent poisons and diseases exist they generally don't exceed a -4 to -6 penalty for resistance. Some do, but not so many. Generally what makes this a bit of a trap is trying to stack side-bonuses on top of high base stats - it's the combo of high HT, high Will, every Resistance you can get, Hard to Subdue, Hard to Kill, and Very Fit. Hurrah, you have a base 18-20 vs. everything and conditional bonuses running from +3 to +8 or more . . . but a base 14-16 and half of those conditional bonuses would have been more than sufficient almost all of the time.
Armor up! - This is the old "get the most armor you possible can" approach. Best, highest DR, most enchanted armor in the game. Start at the top and don't look down. Also get as much natural DR as you can. Harass the GM endlessly about special armor for any locations below your maximum DR. Ask if you can wear 2-3 pairs of gloves and put oversized sollerets over your boots which you have on top of steel-soled slippers.
Why it is a trap - The trap here is that heavy actual armor is going to restrict your ability to move (Move is reduced by encumbrance - and so is Dodge), . This one I see the least often - my players have always had a sharp eye for the tradeoff between movement and DR. Low move on a tactical map means the fight goes on without you most of the time, unless someone really wants to come and attack you. The counter is higher ST, higher Lifting ST, and higher Speed or Move . . . all of which are useful, but aren't free. Also you might see more DX to absorb the -1 for layered armor and offset some of the penalties to Stealth and Climbing. Points you are spending on Lifting ST and better Move to reduce the effects of your high armor are, in effect, being spent on getting some gadget-based DR.
Natural DR is limited, but it's almost always the very first buy for those who can get it. The progression is, buy as much natural DR as you can, then buy the rest before you branch out. Not a bad choice, and you always want this eventually, but in the short run it's got the opportunity cost of not improving other things.
Meta-traps here are that if everyone has a lot of DR, the bad guys get stronger offense. It will happen, because otherwise the game is over (no threat, no risk, no fun, IMO). So in a way very high DR means foes either are very good (to aim for weak points), very strong (to defeat DR), or have armor-ignoring attacks. This might seem unfair, but I can tell you it happens - check out Doug's post on armor, where he posits a baseline ST 14 for determining the effect of GURPS armor. Back in our 100-points-no-disads Man-to-Man days, a ST 14 guy was pretty awesome, having spent 45% of his points on one stat! And yeah, DR 6 was high back then. Escalation happens.
This leaves aside Luck. Luck isn't terribly expensive, and it's actually a good argument against this trap of trying to be immune to everything - it gives you three chances at a roll, which counts for a solid bonus to any roll you need. It can bail you out when even maximized HT, defenses, etc. fail you. If you get a do-over or two, you don't also need a 98.1% chance of success on all of the rolls.
(Aside: Someone mentioned giving a discount for defensive-only Luck. In my games, that's barely even a -5% limitation, since everyone saves Luck to undo critical hits, re-roll failed Death checks, and otherwise stay alive. I've seen Luck used offensively, but it's rare. One odd behavior, though, is the "run when I'm unlucky" approach. It's not that common, but you'll get people who takes great risks while they still have a use or two of Luck, who then refuse to take risks until it is back.)
Ultimately, all of this is sensible behavior . . . except it's spending from a limited pool. Points spent on pushing defenses, armor, resistances, death checks, etc. to "only fails on 17-18" comes from somewhere. Given unlimited points, you may as well have maximum Will and HT 20 and levels of everything. But no one has unlimited points. Even 1600 point superheroes run out in the blink of an eye during chargen.
It's very expensive to be tough. It's extremely expensive to be tough against everything. Even then, you are never totally safe, even with active defenses layered over passive armor over immunities over high stats bolstered by advantages with a Ridiculous Luck umbrella over the whole thing. It's never really enough to fully shield you in combat. Or from direct physical or magical harm. It just makes it less likely. You get to be extremely survivable, until something comes along you just can't hack - a critically successful offensive spell that one-shots your guy, a trapped room with no air, a demon lord with Death Magic, whatever. You aren't buying immunity, you're buying better odds against a diminishing return on investment.
Yet points spent there are points not spent on offensive firepower that might be needed to win a fight. Or social skills to get out of one or better leverage your opportunities in town. Or spent on outdoorsy skills that let your adventurer move about the badlands and haunted woods with aplomb. Those points are Allies not purchased, depth of skill ignore, and so on.
That's the real trap, here. It's having Parry-20, Dodge-14, lots of DR, HT 14, Will 20, a pile of resistances and HT-bonus advantages . . . and rolling against Swimming-12 or Survivial-11 or trying a contest of your Boating vs. the escaping bad guys with your default roll, because you didn't have the points to waste on them. It's having a tremendous Block but being hosed when you are grabbed from behind because you have 1 point in Wrestling. It's having a net -5 to reaction rolls because you are an Overconfident guy with a Social Stigma and no Charisma, no Reputation, no Rank or Status. Points aren't unlimited, and there are a lot of things to roll for and roll against that benefit from actual point investment. Opportunity costs are the entire basis of the point-buy system.
So that's another thing I see in the way of caution - the temptation to spend, spend, spend on risk-reducing and consequence-reducing abilities in reaction to perceived lethality.