Your manager remembers who covered and who vanished. That memory becomes your next reference.

People keep a quiet record of who helped when it was inconvenient. Covering a shift nobody wanted, staying when it got busy, answering the phone on your day off: these get stored in a way your actual job performance often does not. Later that record becomes a sentence someone says about you to a stranger.

Say yes to one awkward ask this month, as long as it does not wreck something that matters to you. You do not have to be endlessly available, and being reliable twice beats being vaguely willing always. When you cannot help, say so early so someone else can.