Be realistic - whatever it is, it will pass. It’s not necessary to understand why something has happened to accept that it has happened. If you can understand it, great, but quite a lot of things in life aren’t dependent on things you do or don’t do and trying to understand those things will drive you mad.
Bad things happen but so do good things. Kipling wrote:
If you can meet with Triumph and Disaster
And treat those two impostors just the same.
Meaning, exceptionally good things and exceptionally bad things are comparatively rare and looking for reasons can sometimes be an exercise in futility. A bird didn’t decide to pose as an agent of evil and target you to take a shit on, all that happened was a bird dropped a load when you happened to be walking there.
In the meantime, do things you enjoy. Go to the pub with your mates, re-read a comforting book, listen to music - whatever. And once it’s passed - because it will - exert control over the things you can control that will make you happy.