Leverage, caution, discipline, and experience. I think the key to being good at trading has been stated time and time again, but it's one thing to read those lessons and another thing to experience them first hand. The journey to being a decent trader really embodies the idea of "easier said than done" because some of the most important ideas in trading are really simple concepts, but there's so many distractions and obstacles that can get in the way of actually adhering to them. I'm of the opinion that you learn the lessons twice. First when you study them or someone teaches you and then again when you experience them firsthand. You just have to hope the first time you learn them doesn't make you so cocky that you lose all your money when you learn them a second time.

That roller coaster heart attack ride you mention, everyone I think has felt that. Occasionally you still do, but it should happen less and less. The mitigation of that feeling should give you an incentive to starting having plans in place for everything. One of my mantras is "the best time to solve a problem is before you have a problem." Figure out all the ways a trade can go, account for as many of them as you can, and have plans in place for what you're going to do in each scenario. You'll still get blindsided occasionally, but compared to the person whose running around with no plans at all, you'll feel really on your game.

Eventually everything get's so mechanical and either because you start managing other people's money or you have access to capital of your own you scale up and have to come to terms with the idea of "win big and lose big." More reward, more risk. I honestly believe the key is just being able to lock in losses quick before they go nuclear on you. When you can do that, when you can say "I will begin closing this position if it loses X no matter what," it's the difference between being able to trust yourself with $500,000 vs $5.