system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do deep sea creatures resist being crushed by pressure, but I could still crush them in my fingers?
gpt
It's not the absolute pressure that crushes something, it's the relative pressure.  Deep sea fish are mostly water on the inside and water on the outside, so if they are acclimated the pressure on their insides is the same as their outsides.

If you decide to crush a fish with your hands, it is a big, quick change in pressure that will crush it as it can't adjust.