At 2.5x the buy-in i turn into a donk....help me figure out why

[varoadstter]

I'm gonna go with choice #1, here. I suspect that even though the money you won and the money you bought in with is the same value, you probably treat the money won differently. Hands that you would fold if you were playing with your buyin are suddenly good enough for you to play since you're up. I'm afraid that I am not immune to this thinking, either.

Another possibility to consider is the impact of big hands when you have a big stack against another big stack. In limit, this doesn't matter but in NL, it's the essense of the game. If you make one big mistake here, you can go broke. Doesn't matter that you spent eight hours building that chip stack - it's gone on one really bad hand (suckout, misread, etc.) to someone who has you covered.

What's cool about the second possibility is that it can work in your favor as well. Many times I spend hours grinding away to get my initial stack to around 2x the buyin and then on one key hand I get doubled up and suddenly you're rolling in it. Such is the way of this game.

In short: leaks, bad - Variance, bitch.