Stuck with models processing

Everytime I write down a model, it seems to be negative. I always get stuck on translating my negative thought to a positive thought and actually believing it. For example “I can’t get this done.” to “It’s going to be done within the time I allotted.” Like, do I just keep saying it until I believe it? Or do I just put my head down and get to work, work my ass off and try and get it done within the time allotted just to prove my negative self wrong?