Should students work on a single problem or multiple problems?

In some cases, particularly when the research is open-ended, it can be useful for the student to have more than one problem to think about. For example, in theoretical research it is possible that any single idea will simply not go anywhere.  Having a second related problem can mitigate frustration and allow the student to go back and forth on these problems until one of them – hopefully – emerges as being promising and fruitful. It can also work well to work on a problem with concrete, achievable outcomes, such as an implementation or experimental project, alongside more open-ended problems.