The first ten meters are where everything hurts and nothing is deep. Your ears pinch, your heart races, and the water is still light-blue enough to show you exactly how far the bottom isn't.

Pressure doubles fast

Between the surface and ten meters, the pressure on you doubles. Your lungs go from 100% to 50% of their volume in the space of one story of a building. No other ten meters in the dive asks that much of you.

Then it gets easy

By twenty meters the freefall starts and the work is over. The first ten are the whole price of admission. Pay it slowly, and the rest is free.