Things die wierdly becase they're probably playing unlagged. Given their ping and the player's movement, from their perspective, the crosshair was over the alien when they shot, even if that's not true for you or indeed the server. That's my understanding of what unlagged is, and makes things more playable on higher pings.
I'm no pro human by any means, but the thing which has single handedly done more for my game than anything else is learning to use dodge effectively. Its unbelievably useful for keeping distance between you and your enemy, and for avoiding pounces/tramples/mara flying headbites. Keeping a bit of stamina available is pretty much essential because of this. Circle/strafe jumping as a human (as per Q3, urban terror, etc) is actually pretty useful for a very quick burst of speed in emergency situations too, even if it uses a ton of stamina.
But yeah, I spec good humans (and aliens) and think "That looks simple now! I really should be able to do that..." then miserably fail to recreate what I've just seen being executed flawlessly.
