I have never had that problem, and in general I don't think it's a real thing. IMO, this is the same sort of thinking that makes people say, "Oh, I had this business idea that I really liked, but I found out there was already a company doing what I wanted to do, so I went back to the drawing board."

There's nothing wrong with answering a question that already has answers if you feel like you still have something to add. Very often those first few rushed answers to a question are either wrong or confusing. Don't be one of those people. Just write an answer in your own time and it will get votes if it's any good. I've gone into questions where an answer is already accepted and highly upvoted, but I felt like the accepted answer was fundamentally on the wrong track, so I wrote my own and it got highly upvoted and accepted.