Don't lose a digit

Yesterday a mountain biking friend was telling my GF about a chain-drop experience of a 3rd party who owns an ebike.
The 3rd party was out riding his ebike recently when his chain came off.
He went to put the chain back on.
Of course we can't backpedal our ebikes because the crank freewheels in the motor, so we have to drape the chain on over the top run of the chainring, then wind the chain on the rest of the way by spinning the crank in the forward direction.
Well, evidently during the process of doing this, while the top run of chain was on the top section of the chainring, this fellow's thumb was between the chainring and chain.
He attempted the slowly turn the crank to spin the chain on, intending to move his thumb out of the way at the appropriate time.
But...
...the motor engaged.
According to our friend, the guy nearly lost his thumb.

Moral of the story:
Whenever we need to put our ebike chain on, we'd do best to turn the motor off first.
=sParty