I don't think people "decide" it's enough.

their's a song that I listen to a lot about self harm (the magicians assistant), and their's a quote in that, something along the lines of

" their's only so much pain you can hold, and recently it seems the tap's been left running"

and I think that's a great analigy

it's like a tap

it's going to overflow and flood the system eventually and their's no going back.

you can't try anymore, because you simply don't have the tools to "clear the blockage"

and naturally it's diffrent for diffrent people

some people can hold a lot of water, some not so much