Is there an idiom for "it was just an example"?

It is one of the scenarios where the expression casting pearls before swine applies.

from CED:

cast pearls before swine ​ to offer something valuable or good to someone who does not know its value:

I'm afraid you're casting pearls before swine with your good advice – he won't listen.

And from Collins Cobuild Idioms Dictionary:

If you cast pearls before swine, you offer something valuable to someone who is not good enough or clever enough to appreciate it.

The expression is from Matthew 7:6:

New International Version {BibleHub}

"Do not give dogs what is sacred; do not throw your pearls to pigs. If you do, they may trample them under their feet, and turn and tear you to pieces.

[Note that this is a chiastic structure, A B B' A'; it is the dogs that might tear you to pieces, and the pigs that might trample the goodies into the mud.)

The metaphor has been further broadened to include anything worthwhile, not just at the overtly spiritual level. The possible unwarranted opposition from those one is trying to help is clear in the complete verse (and implicit in the usual shortened form).

So "I must remember to be careful not to cast pearls before swine," preferably not in the other person's hearing.