Glue needs time to hold. So do new habits. Lean on either one too early and it slides.

A new habit is not load bearing for a while. It looks like a habit from the outside after nine days and it will not hold weight yet, so a hard week leans on it and the whole thing slides off. That is not weak character, it is a bond that had not cured.

Protect the new one from stress for a month. Keep it small, keep it at the same time, and do not add a second one on top while the first is still setting. If a bad week comes anyway, restart without ceremony rather than treating it as evidence.