I used to think like you, until I started a company to work on something because I felt like it was a "useful problem" and it crashed and burned quickly because

I used to think like you, until I started a company to work on something because I felt like it was a "useful problem" and it crashed and burned quickly because I was not truly motivated: I was thinking with the head not the heart. Then I started working on a problem space I enjoy out of sheer technical fun (VR) and have been amazed to discover that it has massive potential for helping solve some of the more "useful" problems you mention. The truth is, when you are working on a project you care about, nobody really knows where it will lead you. Big things start out small and usually with humble ambitions. Usually the things that end up impacting the world start out as being considered "useless" and "toys." I say, work on interesting problems that you feel good about working on but most importantly enjoy working on. Feeling like the thing you are working on is an important problem to solve is a necessary but insufficient condition to ensuring you will get through the tough parts. Richard Hamming once wrote that he asked his peers the question: "Are you working on the most important problems in your field? If not, why not?" And I think this is a valid question and not a leading one at all. But it also is fair to answer "No" to this question if you are able to clearly answer "why not?" to yourself in a way you can live with.