If I was Alice's employer and valued her (and other employees) being able to do deep work, I'd have a policy whereby employees could schedule do-not-disturb time (large blocks of it, depending on their needs) where they could shut their doors and turn off IM. Have a red light on the outside of the door, like a film production booth. Book end the day. First 1-2 hours are disturb time. Middle of the day is DND time. Last part of the day is disturb time.

All scheduled meetings have to happen in disturb time.

Now, that doesn't really work for a customer-facing role, at least not without the cooperation of your customers, but having managed a customer-facing team before, I'll say I encouraged my people to schedule office-hour time with their customers to try to channel the interactions in a more predictable period of time.

Email

…Don’t check it during your DND time…

…Set an expectation that the turnaround time for an email response is 24 hours…

That's exactly the question.

My solution is: Bob should try to ask with moderation, and Bob and Alice should work together in a situation where Bob does not need to distract Alice. If Bob needs to distract Alice, then Alice just needs to live with it. If Bob has questions but does not need to distract Alice, then Bob should not ask the question and just needs to live with it.

What confuse me is that some people here just answer: obviously Alice is right and Bob is wrong, all the time except exceptional cases.

I believe we should examine why Bob needs to distract Alice on a regular basis, and attack that problem with the might and fury of 1911 raging bulls and 420 mosquitoes.

> What confuse me is that some people here just answer: obviously Alice is right and Bob is wrong, all the time except exceptional cases.

Joking aside, I do agree with your point. It's not black and white and there shouldn't be fear/hostility connected with simply asking a question. However, 100% being open to questions all the time is simply disruptive for everybody.