That's not just a problem with teaching, it's the entire problem. Understanding both these things will be true at the same time requires maturation or emotional discipline, which it's not yet taboo to describe as learned behaviors.
> The problem with teaching people when they’re in a moment of profound weakness is there’s an implied demand: my advice is rational, you aren’t in a rational state of mind, choose one.
You’re just making the demand explicit. It’s still a demand, not a fact.
Edit: to be really clear, this attitude that you have rational advice and I’m irrational is a way to ensure that any approach you take that shows any hint of it is suspect. You may believe it all you want, you might even be correct, but I’m just getting manipulation signals.
Humans are irrational. Irrationality can be managed, understood, and harnessed. Don't pretend that grief is an impenetrable weapon against rational thought.