I peaked too early.
I haven't trained enough.
I didn't do enough bricks.
I didn't put in enough volume.
It was too hot.
The field was too competitive.
The course was too difficult; if the course had been flatter, I would have killed.
We all make excuses. I try to keep mine internal, as much as possible (so as not to annoy certain people). But at some point, I have to look at myself, look at my times, look at my training, and admit that I'm not where I want to be, and it's my fault. Not in a self-deprecating, guilt-ridden way. In an I'm-responsible-for-my-own-actions way. If I don't put in enough volume, if I don't train enough, if I don't do enough bricks . . . that's my responsibility.
And knowing that, I am empowered to change.