Your opinion of yourself after one bad game is a sample size of one.

One performance tells you almost nothing, and yet it arrives with enormous emotional authority. A single bad game contains the weather, the referee, what you ate, who you were marking and whether you slept. Reading your whole ability off it is like judging a book by one sentence picked at random. The pattern across ten games is the thing worth looking at.

Resist filing the verdict tonight. Write down what specifically went wrong, in two lines, then go and look at the last ten. If the problem shows up in eight of them, you have found something real to work on.