What does the phrase: “eaten bread is soon forgotten” mean?

It means that “once it’s gone, it’s over”, i.e., after you’ve finished consuming something, it’s not what you’re thinking about any more. I’d have to have more specifics to see how it was applied in the situation you describe.

It’s rapidly digested, but I don’t know about the wider context, since one must eat to live. Saving it and not eating it does you no good either since it will grow stale.

It basically means whatever instructions were just given no one will remember in a minutes time. Maybe they were too complicated or there were too many at once. That’s what I gathered from your question.

The authors intended meaning is that recipients of charity or assistance quickly forget who helped them when their immediate need has been satisfied.
Thomas Fuller

It means “What have you done for me lately?” or that people soon forget about what’s been given to them if there’s not some specific reason for it to be fresh in their minds.

It means that something earned and consumed is forgotten, quietly alluding to the importance of remembering how something was gained, earned, or fought for in the first place. Essentially, do not forget where you came from.. and by extension.. where your car, your spouse, your property, or your money came from. Remember and continually appreciate the climb to the top of the hill.