built a tool for one client, now other people keep asking for it. wasn't planning that

so this wasn't supposed to become a thing. one of my clients teaches german, runs a small school, and he's good at teaching but never had time to post on social. He told me he wants to spend less time creating posts

built him a thing that writes posts in his own voice and posts them for him so he doesn't have to bother. thought it'd be a small side task.

few days two posts brought 1.3M views and he got like 250 followers out of nowhere. figured it was a fluke.

then other people started messaging me asking if i could set the same thing up for them. wasn't even trying to sell it, they just saw it working and wanted it.

kind of funny because i spent ages before that trying to build stuff people might want and nobody cared. built one thing for one actual person with a real problem and suddenly there's demand i didn't go looking for.

anyone else had this? built something for yourself or one client and it accidentally turned into a product? how'd you decide whether to actually run with it?