New here - how do you actually stick to your trading plan?

Been dabbling for a bit, mostly on $SPY and $QQQ options. I've got a decent plan laid out – entry criteria, profit targets, stop losses – all written down. The problem is, when I'm in a trade, especially if it starts going against me or rips quickly, I find myself second-guessing everything and either moving stops or bailing too early. How do you guys actually develop the discipline to just execute the plan without the emotional interference?