Does Therapy work?

I know this is probably too much to put on one comment but my family is going through a lot and I’m trying to not be a “f@*k up” son... I (18M) started therapy months ago because my sister (14F) got diagnosed with ADHD, a year ago, and I am doing research to see if therapy can help a lot? and the results are mixed... My dad keeps saying that it is hard to work when you are not motivated and I’m starting to believe that Therapy can be a waste of time and money? He has been saying that a lot lately...