I was eating vegan burgers every so often. That should've covered the psychology aspect, but it didn't.
My energy level was steadily declining, as you might expect for an iron deficiency. When I gave in and started eating burgers, they were profoundly tasty, and my energy levels recovered.
I've had dietary shifts in the past (from one omnivore diet to another) and nothing like this happened.
I'm on board with the ethical aspect of veganism. I'm annoyed by what I perceive as the ideological aspect, which pretends a vegan diet can easily be perfectly nutritious.
[I'm complaining about this because I'm hoping vegans will take a hard look in the mirror, and start taking nutrition seriously, so I won't suffer from an iron deficiency (or whatever it was!) if I try again in the future.]