There’s a kind of hermit crab that dies if it doesn’t find a bigger shell.
Its soft, vulnerable body grows slowly over time, until the shell that once protected it becomes a claustrophobic prison.
When this happens, the crab must leave the comfort of its current shell, venture out into the dangerous open, and risk being exposed, naked, unarmored, and killable while it searches for something bigger, something better.
The crab has no choice as if it delays too long, it will be crushed by its own growth.