Sure, the concise version is that I had an essential biology assay not work for three years running. It meant I couldn't do much to generate results. The pressure got to me and I burnt out hard. For whatever reason, the support network I had (including excellent supervisors) wasn't sufficient to overcome or work around the problem.

Looking back, diversifying my work and finding short term projects likely would have innoculated me against the effects of the (biggest) problem I faced.

After leaving, I have had few regrets (aside from lessons learned). I have had fun jobs, travelled, and had far less stress holding me down. Less money, sure, but more of the really important things.