system
Given the following post, respond as if you're commenting on Reddit:
human
What is the truth behind the threat of "skipping off the atmosphere?"

In space movies, when the brave astronauts are about to re-enter, you often hear someone very solemnly pronounce, "If the angle of re-entry is too shallow, the capsule will skip off the atmosphere." Back on Earth, the astronauts' families cringe in fear, with the implication that this terrible thing must never happen.

What is the reality of this? Have any of our spacecraft *actually* "skipped off the atmosphere?" If you did "skip off the atmosphere," where exactly would you go? Is this something that could be harnessed productively, like to provide lift or change course? Or is it just some movie metaphor?
gpt
What skipping off the atmsophere really means is having a trajectory that takes you through the upper atmosphere, which is curved like the Earth, at a speed and angle that atmospheric drag isn't enough to terminate your orbit. 

It is a very real threat. 

But can also be a tool. You can use a shallow entry to make several passes before your intended de-orbit to slow you down for a safer re-entry. 

But you're not likely to go barreling off into the unknown because of it. You'll more than likely remain in Earth's sphere of influence and your orbit will bring you back around again. The trouble then is mission length. You're not coming back around quickly and whatever oxygen and such you've budgeted for the mission will likely be exhausted. So your ship will make it home, eventually, but it'll be a really expensive coffin at that point.

We actually designed a few missiles to make use of this to save on fuel, 'skipping' around the globe.

No manned vessel have ever done it and Apollo 13 came the closest with a pretty shallow entry.

Edit: It helps to realize that 'skipping' is a bit of a misnomer. Objects don't skip off atmosphere the way a stone might skip on the water. The stone does this because of the properties of water and the stone generating lift. No lift is needed for atmospheric 'skipping.'