This question already has an answer here:
I understand that every 10 feet of distance fallen is 1d6 bludgeoning damage at the bottom... but how do you determine when to start calculating that if a player intentionally jumps down from a ledge? At what point does "dropping down" become "falling"?
I don't think it's based on the jump range measurements provided by the PHB, because the vertical distance is almost always less than 10ft, and the jump distances seem to be just an allowance to bypass terrain obstacles during your move by jumping over them.
Ten feet isn't that high and, while it can certainly hurt, 20 feet didn't kill me or break any bones. I expect more physically capable people would be able to jump down from higher, but I wouldn't dare do it myself — 20 feet was scary enough.
Clarification: In the absence of magic. How high is "a great height"? When dropping down, the only distance restriction is how high off the ground you are. Another example of this could be an aarakocra who chooses to drop from the sky to his feet, rather than flying down and landing. It's controlled because they chose to jump, so does that mean they're immune go damage regardless if height? Just because they wanted it? By that reasoning, saying "I meant to do that" could save your life. Is it just 10ft or more automatically becomes a fall unless magic is helping you? That seems totally arbitrary and random.