What's your bus factor?
List the critical knowledge areas in your project. For each, mark who understands it. The areas with only one name are your single points of failure.
Knowledge area
Project bus factor
What to do about a bus factor of 1
Pair programming, documentation, and cross-training are the standard advice. But the real fix is structural: no critical system should be the sole domain of one person for more than three months. Rotate ownership deliberately. It feels slower in the short term. It prevents catastrophic knowledge loss in the long term.