How do hydraulic flat tappet lifters fail?

Come to think of it, it did take a few tries to get it to start because the timing wasn't quite right. Once it did start, we took it right up in RPM. I'm starting to think it was me who caused this failure.
While it might settle your mind to know exactly why it happened, it doesn’t really matter. Make a plan, learn from the experience, and move forward. It’s something a lot of us have done. Just adapt and overcome.