12.23Idempotent update vs non-idempotent increment

This is a useful distinction.

Idempotent:

set balance = 100

Repeated:

100
100
100

still 100.

Non-idempotent:

increment balance by 100

Repeated twice:

200

So event design matters.

Prefer:

CustomerBalanceChangedTo 100

over:

Add 100

when semantics permit.