Everyone has some form of problems. Or you are not living. They may not be constant but seem to be unavoidable.

One can have problems to a lesser or greater degree than others. I do agree the fewer the better. Ones tolerance level for issues develops with the experience of them. No two people will be the same.

Einsteins theory of relativity may apply in an oblique fashion. We are all defective. When in general happy we really are not fully aware we are. Yet when unhappy it can be the epicenter of our very existance.

Defining the difference is very hard to impossible. As it is so subjective in nature I suspect. Genetics are probably involved.