I think it applies to any project, not just open source ones. When the going gets tough, and it always eventually get tough, you'll need personal interest or passion to get you through.
Projects which help in earning your living will do fine. You'll probably end up working on it everyday. On the other hand, it's harder to find time for projects which are not related to how you make a living. And, if you struggle to find time for a project, then it's going to be hard to sustain it.
Opensource projects typically fall in the latter category. The ideal situation is if you manage to establish some sort of connection between your pet project and your source of income.
Opensource projects typically fall in the latter category. The ideal situation is if you manage to establish some sort of connection between your pet project and your source of income.
edit: typos