Which Trading Rule Is Hardest to Follow in Real Time?

Rules are easy when the market is closed.

The real test comes when price is moving, P&L is changing, and emotions are involved. That is when a simple rule suddenly becomes difficult.

For me, the hardest rule is waiting for confirmation. I can know that confirmation matters, but when a stock starts moving fast, the fear of missing out kicks in. Suddenly, entering early feels reasonable.

That is usually when I remind myself that a missed trade is not a loss. A bad entry can become one.

Other traders probably struggle with different rules: stop losses, position sizing, patience, taking profits, or avoiding revenge trades.

Which trading rule is hardest for you to follow in real time?

And what do you do to stop yourself from breaking it?