Brick Walls and Dotted Lines

What does it mean, exactly, to "Cross the Line"? Is there really any line which can be "crossed"? And at what point is it that it counts as "crossing the line"?
This is sort of a tricky subject. You have to make boundaries, and know your limits, but life is rather fluid. It's not some set of rigid rules, like a mathematical proof. It's fluid, flexible, constantly changing, never really quite the same.
So there really is no right or wrong answer, no brick wall that says "Thou Shalt Not Pass." Not even a dotten line, a suggested stopping point. Because both of those stay in the same place. It's more like a string, where you can push on it to deform and reshape the boundary, adjust it to your liking. Each person's boundary is different. The only real trouble is figuring out exactly where to put it, where's the stopping point, how far is far enough? And the only real substitute for that is experience.
So I guess all I can really say is know your limits. If it's your Moral Limits, try to keep them almost constant, try not to go too far into the other end, make sure you lay your string down and keep the fickle winds of Society from blowing it too far. If it's your Personal Ability Limits, push the string, stretch the string, move the string, break the string. Do your best in everything, and let everyone else worry about the "limits" thing.
Keep your eye on the string.