Subject matter experts are silos - subject matter expertise needs to be shared. If experts are leaving a project, the subject stays. By then, if you are not able to close such a gap from within your organization, expertise needs to be bought from the outside. There is only one profound way to come around the problem: don't make people silos by making them subject matter experts.
What makes up a great scrum master? Test yourself and take a close look how you or your team is perceiving the daily routine.
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