Some people think stopping because they are up for the day is smart money management, but they are wrong.
If your trading conditions are met and your money management rules allow you to trade, yet you stop because you do not want to give back your profit, you are prioritizing "ending today with a win" over repeating your system.
And if you take the relief of thinking "I am glad I stopped" as proof that your decision was right, you strengthen your belief in protecting immediate profits and become more inclined to depart from your rules for the same reason next time.
You are playing a game of wins and losses, not a game of probabilities.
You may think it is good that you protected your profit, but through that action, you are training yourself to place greater importance on short term wins and losses.
Probabilistic thinking means accepting both the wins and the losses of a system with an edge and seeking profit across the full series of trades.
Even if you understand that intellectually, prioritizing today's win through your actions develops the opposite way of thinking.
Of course, stopping according to a rule you tested beforehand is a different matter.
The problem is putting your desire to protect today's profit ahead of your rules.
If you want to play the probability game, do not reinforce the game of wins and losses through your own actions.