I think this is a question everyone should ask themselves periodically. Everyone should take a moment to reflect on what they're doing, why they're doing it, is it worth it? Sort of looking up from the path you're on to look ahead and make sure you're going the direction you want to go.
These rough times are automatic reminders to ask this question... what can be even more dangerous is when things are going really well according to external measurements and an entrepreneur doesn't feel like they can ask that question.
Not only do I think every entrepreneur should ask them selves this but I think if you're not doing what you love, and you know what that is (whether your an entrepreneur or not) the question is "What's stopping you?".