If I hire someone to do something, and they do a bad job, I have to beg them to come out and fix it, if they even will at all. And they're the only one with the knowledge and experience and tools to do the repair, so I feel frustrated that I'm unable to resolve it, its going to be like that forever.
If I do something myself, now I've learned how to do it, and buying any necessary tools and equipment to do it was probably cheaper than hiring someone to do it. And if I do a bad job, I console myself that I could fix it if I cared enough, even if I never get around to it. At some point it'll annoy me enough that I will fix it, or it won't and I won't care. Personally, I find this to be much better for my mental health.