2, 3, 4, . . . .n lines of position

It depends on your distance from where you are taking your fix and what you consider reasonable. I learned to sail in the Yellowknife bay, and at the entrance to Yellowknife Bay are many many submerged rocks, and simultaneously, not many good places to take a fix off of. I bought a GPS because I felt that a "reasonable fix“ was impossible in those circumstances. But most days I didn't even bring it because I was staying in the safety of the bay, where a "reasonable fix" was simple line of sight (didn't even bother with a hand bearing compass, I just looked around with the MKI EYE). Enough fixes that you are confident that your boat, and everyone on it, is safe: I've read about dogleg coral cuts where all the fixes in the world won't replace a man up the mast, and I've read about sandy lagoons where no fixes are required. Anyone who says "2 is enough" or "6 is too many" simply hasn't sailed in varied enough locations is all.