Intrusive thoughts

I feel like life is just part of something bigger that we are going to experience, as life is just a part of the whole way that we are going to cross. That every feeling is a really small part of what we will feel in the future. I like to think that every obstacle that appears to us, its possible to go through it. As (God, in my case) will not give you anything that he knows you can't go through. So even though life feels terrible sometimes, at the end it will be fine, and we will look at it and laugh and be proud of us because we were capable of doing it. But why, if I know all of this, why can't I believe in my own words, why do I keep being anxious about everything that is going on? Can't answer this one