I think one of the things that can really mess up your life and affect you negatively is your expectation of how life should be.
Painting an image in your head of a scenario or how things will go. But the fact is you can't control life... and you can't control other people. and that is one of the things you need to learn to accept, that life won't always go as you had planned or thought out.
Sometimes you think, I'm ☓ years old and I've achieved nothing, and look at all the people the same age as me who have achieved so much. But everyone is different, everyone has different lives and opportunities. .. some need to work harder than others. You shouldn't compare yourself to others. That will just make you feel down and feel like your life isn't good enough.
There have been times where I have thought out and planned how certain events and scenarios will play out, but things never go as I had planned. People say different things, behave in different ways or other things. For example, when I felt ready to talk to my doctor about my current situation/feelings and then I have a random new doctor who is mean to me and threatens to admit me to hospital (for CF reasons).... not exactly how I had planned to tell my normal doctors how I felt and that she would be understanding and help me.
Or when I maybe plan to have a movie evening with my sister and then she doesn't even want to... or I don't want to watch movies etc etc etc
Also remember, people don't always act the way you had thought they would. Such as if you are sad and start crying and just want someone to hug or talk to, not everyone will understand that and some might tell you to snap out of it. Which is wrong... but people behave in different ways. Such as people show they care for someone in different ways. Some are more verbal and others show in small gestures or such. Just like people show sadness or anger in different ways and once again, might not act like you had thought they would.
It's hard to not plan put scamenarios in your head and plan how things will go. But just remember, it won't always go as planned and you need to be ok with that. Life goes on and that's part of life, the different and unexpected. Don't feel sad or angry just because things didn't go as planned, you can't control life and you can't control what people, how they behave or what they do. You can only control yourself.