A popular business expression goes “Underpromise and overdeliver.”
But I can’t think of a single important relationship in which that is the best approach.
Do people underpromise in their wedding vows? Do parents underpromise to their children? Do you underpromise to your friends?
Underpromising is always, to me, a subtle lie. It’s asserting “I can only do this much” when in fact you know differently.
I never want to be guilty of underpromising to my students. I’d much rather say, “Here’s what I want to achieve” and fall short, while being always honest. I’d rather define reasonable goals, stretch goals, and nearly-impossible goals, and work on them together. I’d rather apologize for coming up a little short than overdeliver and admit to lying about what is possible.
In short, a much better expression is “Overpromise and deliver as much as you can.”
Will students occasionally be disappointed? Sure – especially in a global pandemic. But I’d rather be disappointed together with my students than any other alternative.