Whenever I catch myself brooding excessively over something, I ask: Is this time spent this way is how you must? Would you not judge yourself that you spent on it More time than it deserved?

If the answer is you won't regret because you wanted to get to know WHY certain thing happened certain way. Note: it's not the same if later you might come to regret having spent this much time then better ask this question to to yourself, and be clear and honest.

Regarding why OTHER people can't understand....end of the world" is something beyond your control. I'd think everyone makes mistakes and KNOWS it that it's not the end of the world. I lost my apt keys some months ago and cost me over two hundred dollars. It wasn't end of the world. I'm sure others will agree too. So I'd not worry if YOU find some are weird. At younger age we can be less cautious with time, including myself; today I KNOW my time is limited, having entered into my 8th decade.

You say, "The cause of my concentration problem is self-blame. I blame myself for my wrong decisions." Do we not if honest would blame Ourselves for OUR wrong decisions? Blaming Others would be ludicrous!
But it does not mean Fretting and ruminating without any conscious purpose. That is waste of our time. Since you said you have "philosophical" disposition, won't your deep thinking lead you into this more mature way to look at it once for all and Move On?