system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What determines whether your belly button is an innie or an outie?
gpt
Winding up with an innie or an outie is somewhat of a matter of chance. While the majority of people have innies, outies usually occur when more of the umbilical cord is left when it's cut, leading to some remaining scar tissue.

Everyone tends to start with outies, but as the subcutaneous fat layer develops under the skin around the umbilicus, they move inward to become an innie.

Some doctors claim, however, that it has nothing to do with how the umbilical cord was cut or clamped. Outies which are not the result of extra scar tissue are typically caused by an umbilical hernia-- when the stomach muscles don't fuse together properly after the cord remnant falls off, causing abdominal tissues to poke through.