As a project risk manager one of your risks is that a member of the team does not know something that they need to know in order to get a task done.
Some people ask for help when they are stuck or unsure. Some don’t. People who do not ask for help when they should are an added risk to your project.
I’d be interested to hear what others do about this. I think pairing is a great way to surface this risk.
When I interview someone for a role I keep asking questions until the candidate says “I do not know” or “I’d have to ask someone else” or some such variant. If they cannot admit they do not know something, they are a very real potential risk to the project. When they know more about a subject than I do, I will get someone else who is an expert to probe their knowledge. The area where you are most at risk is in their area of greatest competence as it is here that they are least likely to ask for help.