Sometimes, this happens even if you are actively using them.

When you have been using finger print for so long, there is a good chance that you forget the pattern or PIN you set a few days ago. Even if you are using a Finger Print lock as primary, you are still required to set a Pin or Pattern as a fallback mechanism.

There are more than a billion users who use the Android Operating System on a daily basis and most of them secure it with the Pin or Pattern lock.