Show HN: I spent 2 years building an iOS app no one asked for

i built a heart rate zone training app for runners. ios + apple watch. custom zones, real-time haptics, post-run graphs. all the “smart” stuff you’d expect. but i never talked to a single runner before building it. not even myself lol. started as a thesis → kept building → added features → added a paywall (€4/month!) → launched it → and yeah… no one cared. zero feedback. zero users. just code in the void. i recently made the whole thing free. not trying to “sell” anything now — just seeing if it’s actually useful, and listening this time. curious how others handle this. ever build something 100% wrong?