Schedule only runs once?

I have a feeling it's because I'm using multithreading, though I'm only using one schedule event. I don't really know what I'm doing wrong, but the event only runs once and then stops (instead of every three minutes or every day). I'm on windows 11 if that makes any difference. Putting the schedule code in another function doesn't help either.

###functions up here###

```
if __name__ == "__main__":
startThread = Thread(target=start).start()
userThread = Thread(target=userInput).start()

schedule.every(3).minutes.do(backup)
#schedule.every().day.at(backup_time).do(backup)
while True:
schedule.run_pending()
time.sleep(10)
```