Why can't I accept the good things in my life aren't going to imminently implode?

I'm completely unable to experience contentment or any happiness. All I do is worry about something blowing up catastrophically.

Fear and worry rule my life. Mostly pointless worry and fear but the feeling of constantly being fearful is ruining my life.

I'm taking this to therapy soon, finally, but I'd really appreciate some insight.

I just want to be able to feel a moment of contentment again. Just for a moment.