Learning when and how to determine the importance of things is something I've bettered myself at, in more recent years. It's very difficult to let some things go to the wayside, especially when you've become personally involved or if something bothering you is present in your daily routine. Even more so difficult is figuring out what all should be minimized in your life and what things you should actively confront, in order to better your situation.
I'm a big lover of heavy metal music, especially death metal and melodic death metal, and I tend to embody the loud, aggressive energy that metal has when I'm confronting something or someone. Given my natural characteristic of holding grudges against people who have wronged me or someone else, that aggression gets turned up to 11 whenever I find myself in a confrontation. One of the two most difficult parts of learning to let something go, for myself, was learning how to temper that aggression and to figure out what level of "mad" was appropriate for a given situation.
My rule of thumb is, "If you find yourself shouting at someone, getting in their face, and gearing up to punch them if they say one more wrong thing, you either need to take a minute to calm down or walk away from the situation entirely." Typically, if you find someone or something that gets you THAT angry, that means that there's either something wrong with you to where you can't confront them properly or that the person you're upset at has something wrong with them and you need to stay away. If it's something besides yourself, you should probably consider disassociating yourself for your own well-being. If it's something in your own behavior that causes you to react so viscerally, you need to take the time to reflect on why that is, where it's rooted in, and possibly seek help in correcting that behavior.
The other difficult part in my process was to learn when to actually engage in confrontation. That was something I had to condition myself to learn how to do after my high school years, given how combative I was in my youth. I had burnt myself out on confrontation to the point where I became avoidant to any confrontation whatsoever. The biggest help in overcoming that hurdle was truly understanding that life will go on after the fight is over. Understanding that everyone involved, including myself, will probably forget about the fight, or at least not feel anywhere near as strongly about it after a day or so.
I had to push past the aversion I had developed for the "jitters" I normally get whenever I confront someone, which took a lot of time and gradually-increasing exposure to heated situations. I also had to learn to develop and utilize coping mechanisms to help myself not obsess with the confrontation afterwards, which was another thing that I had dreaded in confronting others. In understand what behaviors I could change and which ones I couldn't, I conditioned myself to pick and choose which situations I got myself in, gauging what level of aggression was acceptable, and figuring out when it was time to drop it.
My challenge to you, dear reader, is to reflect on the times you've gotten into confrontations, how you reacted, and your behavior after the confrontation was over with. If you find yourself obsessing with what was said for days after the fight was had or if you find yourself being timid when it comes to engaging in confrontation, I also challenge you to learn how to let things go. Confrontation, in and of itself, is not a bad thing and can actually be healthy. It's a method of establishing communication when other efforts to do so have failed. Learning how to do so is integral for all aspects of your life and I encourage everyone, whatever their hang-ups are, to learn how to let it the fuck go.