A trading journal is a record of facts, not feelings. Logging entry reason, stop price, emotions, and outcome reveals your unconscious patterns as data.
Behavioral Economics Basis
Hindsight bias leads us to justify decisions after the result is known ("I knew it all along"). A journal lets you judge yourself on "did I follow the rules?" rather than profit/loss. Many prop firms and institutions mandate daily trade reviews for this exact reason.
How to Start Small
A few lines a day is enough: why you entered, whether you honored the stop, and any emotional spikes. This alone yields massive insights during weekend reviews.