In the formal business language of project management, there is a concept known as 'bus-proofing'. Among technical communities, it's called 'raptor proofing' based on the 1993 Classic Jurassic park.
Think of it like this. If the only person who knows how to do a task ends up in a situation like this
...and the only other person who could possibly figure things out is a little busy...
So we ask ourselves, how is the project going to endure if Lex gets eaten?
No matter how improbable it is to be eaten by genetically engineered dinosaur-like creatures, struck and killed by an asteroid, or drive a bus of a cliff, the lesson remains- document, back up, and train a project understudy's or two.