Have I ever made mistakes in choosing article topics? Yes I have. Here are two examples.
Symposium invitations present a special problem. “Write something about X” does not generally lead to great work unless it happens to fit something you are already doing. Sometimes, though, you accept the invitation because a friend asks you, your home law review asks you, etc. I would say that my Symposium pieces are things that I would have not have otherwise chosen, with maybe two exceptions. But I’m sure I’ll still do other symposia.
One regret is that a decade ago I started writing an article on the unwritten constitutional principle of central bank independence. I then decided: “Eh, this will never come up in actual case. It’s too well-settled.” Oops.
One final note. A paper that you abandon is not a mistake so long as you cut your losses soon enough. You learn from those projects and eventually end up using some of that material in other papers.