If you are not used to taking impacts from jumping from high places (e.g., typical sedentary person), you will almost certainly sustain a severe injury.
Broken and dislocated ankles and ligament ruptures are alarmingly common. Dislocations are especially bad, because the ankle's blood supply isn't great to begin with, so a severe dislocation is like yanking a plug out of the wall; if the blood supply doesn't happen to get re-established (which even microsurgery can't do anything about), you are looking at avascular necrosis. Imagine a dead coral reef crumbling away.
It's even worse in climbing shoes because your toes are crammed together -- imagine landing on your fist.
Rock-climbing (roped) gives your feet and ankles time to strengthen as you support your weight on tiny toe-holds, which is a slow process because ligaments and tendons have poor blood supplies compared to muscles.
Looking at elite climbers bouldering is like looking at elite gymnasts -- you don't see all the ones who got seriously injured along the way. You see them taking 20-foot highball drops and think, how bad can 10 feet be? Or 5 feet?
Even a drop of a few feet can result in a severe injury if your foot isn't flat; when you are jumping off backward onto a lumpy bouldering pad, if your foot lands inverted slightly, the impact can force it inward 90 degrees.
This probably happens twice a week at popular climbing gyms with bouldering areas.