Of course, motivation is an important issue in choosing a sport. If you start running, it might be boring and not very satisfying, so it is hard to practice regularly.

But I think from a huge extensive list of sports, a lot of them can be discarded for being too risky (maybe soccer or mixed martial arts?), having no physical/mental health benefits (maybe most e-sports?) etc. So I do not think that "Whatever you can get yourself to do regularly" provides a sufficient condition for finding out whether a sport is rational, even though it is definetely a necessary condition.