Did you ever make a mistake with your blog niche?

Did you ever make a mistake with your blog niche?

One time I started a blog for purely money reasons, because I thought that topic would make a lot of money. After all, there were others in the same niche that claimed to be earning well from it. I learned very quickly that what works for some will not always work for others. Either that or the others were lying about the profit potential of that niche.