Here's a game I lost recently. I thought I was doing well untill the the end of the middlegame, but I think what it came down to was a failure of attacking well.

I played black. Comments please!

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"There are no limits. There are plateaus, but you must not stay there, you must go beyond them. If it kills you, it kills you. A man must constantly exceed his level." -- Bruce Lee

Some comments:
16: Looks wrong, at 18 your stone is already damaged. It is probably a move that only works if you are very strong at the top (which you are not).
27: I don't think I need to explain why this move is bad, White punishes it well enough in the game anyways.
37: This is too slack given your thick F2 group. K4 is a must. After W pulls back, the bottom is overconcentrated.
47: The timing behind this move is not correct. Q10 is more important.
63: Why try to make living space so painfully when you can just move out? It doesn't even make a base that guarantees two eyes -> this move is too slow.
67: Simply extending to P12 is better.
91: Just extend.
93: This move is too greedy, do you really expect to kill this? White has more than enough room in the center, and there is still bad aji around P9. Better off trying to kill a lion with a BB gun.
121: Too slack, even O9 is better.
125: S18 is clearly bigger.
151: Thank-you move that forces White to do what he wants while you get scrap.