Ask HN: At what stage of your start-up would you quit college?

Leaving University/College is not a decision to be taken lightly, especially if one is near the end of a course and has accumulated substantial debt. Even if you have great personal belief in your start-up it would be unwise to quit without some initial traction. What would be the key trigger in your decision? For anyone who did decide to drop-out, at what stage in your growth did you decide to take the plunge?