I had two pretty funny ones back when I started to solo Gold. Both times in wave ten I said to myself: "be careful, first order of business: kite the enemy away". First death came by a Banshee maybe three seconds into the objective wave, because I changed my thought process just a little bit into "well, let's jut look around this corner to see how the situation is and THEN you kite the enemy away to have an easy walk with that drone". HOW the situation was? Banshee right around the corner, grabbing me instantly!
Another try back in the day ended after just one second in wave ten. No gels, no cyclonic mod, having been sync-killed by that Banshee not too long ago at that time, I changed my thought process in a game against Geth just a little bit: "let's just look around the corner..." Well, around that corner? A Prime ready to shoot... (to this day I refer to this scene as "the Prime instant kill)
The lesson: instead of foolishly looking around corners in solos, what about the Geth Scanner? Idiot!