It is not a problem if you are a student learning how to solve problems. Solving previously solved problems is often a good way to learn - because there is a solution you know you are not hitting something that cannot be solved, and your teacher can guide you if you get stuck.

For real world everyday problems normally it is an application of already solved theory or it isn't worth working on at all. We still need researchers to look at and expand our theory which in turn allows us to solve more problems in the real world. And there are real world problems that we pour enormous amounts of effort into solving despite lacking theory, but these areas move much slower than the much more common application of already solved theory and so are vastly vastly more expensive. (this is how we get smaller chip architectures, but it is a planet scale problem to solve)