@Siebe: What you said in the above:
“A bit salt in not much water will give very salty water. But the same amount in a river cannot even be detected. This is mentioned in AN3.100 (numbering Bodhi). Thanissaro numbers AN3.99:
Lonaphala Sutta: The Salt Crystal
That is correct with regard to any situation, not only in this particular case. And that is an important point. When one habitually does many punna/kusala kamma, they accumulate and tend to dilute the effects of any occasional papa/akusala kamma.
In addition to the examples given in that sutta, we can consider the following too: When a $1000 check bonces off of an account at a bank, where one has only $500 in all accounts at the bank, that is a big problem. However, if that person had a million dollars in another account at the bank, then that is not a problem at all.
Another example similar to the one is the sutta: Sometimes we see standing water in a ditch by the roadside. It could be discolored and even smelly. However, when a good rainfall comes, all that dirty stuff will be washed away. The Buddha called this “rivers of punna/kusala kamma washing off many small accumulations of papa/akusala kamma“.
When one has “a lot of reserves of good”, an occasional misstep or misdeed is not going to affect the overall situation.