Anything I think about never happeneds

I don’t know what this is or if anyone else has experienced this but I need help. Whenever I think of something (good or bad) could be anything 99% of the time it will NOT happen unless it it’s the inevitable. It’s gotten to the point where I’m trying not to think of good things because I genuinely believe it won’t happen if I do. I just need someone to explain what this is and how I can stop it or something.