What are some subtle examples of the difference between necessity and sufficiency?

Question

What are some subtle examples of how the difference between these two things can greatly impact the meaning of a sentence, discussion, or conclusion?

Answer 1

The standard example for the difference between necessity and sufficiency is "the rain, the sprinkling truck and the wet street":

Raining is sufficient that the street is wet. But raining is not necessary that the street is wet. Because operating of the sprinkling truck in the dry season is also sufficient for the street to be wet.

Aside: Why do you ask this question? You have just edited a similar question necessary versus sufficient.

Answer 2

Typing one's answer is necessary to respond to a question on this site, but it is not sufficient- the 'Post Your Answer' button must be clicked too.

As for subtleties, I wonder how long it will be before someone points out that typing isn't necessary because you can ask Alexa to do it!