I agree with Mitch and think this is a great question that we should all reflect on from time to time.
To keep it simple, I think to an extent it means being okay with "having two (or more) people work on one task" for a certain period of time - one to teach and check, and one to work. Over time, the teacher/checker should ideally be able to play a lesser role and only end up being needed for situations that the new person/people haven't encountered yet. Or, since you specifically mentioned avoiding single point dependencies, the task work is split between multiple staff members going forward.
It may not even "cost more" if you can train two people to each work on half of two tasks, though I realize this is not always possible. The alternative is that we may need to accept that optimizing staff-allocation on a task is in opposition to creating redundancy.
Formal or informal task documentation is also helpful in certain cases as well, particularly if these are treated as living documents which are frequently updated and their importance is recognized by both the new and old staff alike.
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Christopher Seigel P.E., M.ASCE
Civil Engineer
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