Share 'How do you decide when an issue of your zine is "out of print"?'

I've noticed that some issues of some zines go permanently out of print after a time. I was wondering how you (personally - I know it'll be different for everyone) decide when an issue is going out of print - do you print a certain number of copies of each issue and then put it out of print? Do you not print any more copies after a certain amount of time has passed since you made the issue? Or is…