Not recording the number you actually got

Without the price at bet time and the price at close, there is no way to tell afterwards whether a result came from good process or good fortune.

The win-loss column is dominated by variance over any period short enough to review. Closing line value is not, which makes it the only field that carries information about the process at short horizons.

It is not a complete answer. A bettor beating the close can still be losing money, and over a long enough horizon profit is the measure that matters.

And that is the trap. Memory is selective in a consistent direction — the prices remembered are the ones that felt good. A log is the only thing that resists that, and it costs nothing.

What to do with it. Record date, market, side, price taken and closing price for every bet, starting with the next one.