I have a finite amount of mental energy each day. Here are my usual ways that I waste mental energy: Jealousy, regret, and self deprecation. These are the equivalent of me grabbing my mental energy and throwing them right into the shitter. This is an open letter to myself on this matter.
Jealousy. Oooh, this has been one of your favorites in the past. Usually, this feeling comes up when you see someone else close to you get what you want. Sometimes you won't even know that you want something until someone else gets it. Other times it's come up with relationships, both romantic relationships and friendships. More often the former than the latter. If a girl you had a relationship with in the past starts dating another guy, then BOOM! You arrive at the height of your jealousy. But all these thoughts are involuntary...or so we thought.
Regret: Often you'll find yourself thinking, "What if I had done things differently?" And that first thought leads into thousands of other thoughts throughout your day on how you could have done things differently, and on thinking about the results you could've had if you had done things differently. But none of it matters, because what happened, ALREADY happened. Thinking about all the scenarios that could have come from you acting differently is wasting energy.
Self-deprecation is usually a result of the last two feelings, and this feeling is the one that keeps the ball rolling on the "mental waste train'. This belittling takes over your mind because: "it's always your fault". And this is true, anytime you don't get something you want, it's always your fault. But, everything is already done, so all there is left to do is learn. Entertaining self-deprecation does nothing for you.
Finally you've come to understand that these three feelings are just indicators for where you have fallen short in your consistency and in your discipline. Yes the initial thought is involuntary, but the subsequent thoughts are not. You only get jealous when you know that you could also already have that THING that the other person has. What you regret is not having had the discipline that they had in order to already get that THING. You self-deprecate only when you don't have the disciple to look for where and how you can improve on yourself.
So the lesson here is simple: allow the initial thoughts of jealousy, regret, and self-deprecation to serve as big fucking arrows that point to where you know you have to be more consistent and disciplined to have the things you want in life. Once you see the message let these feelings go and get to work.