Don't beat your goldfish because it won't fetch your slippers

Don't beat your goldfish because it won't fetch your slippers.

If someone is clearly not the right person for a certain task, don't keep punishing them for not performing.

Someone was asking me about a business situation where someone was neglecting something that I thought they should do.  She was surprised that I wasn't fighting this.  I responded that there was no point in fighting it, because the person didn't believe in it, wasn't equipped to do it, and wasn't interested in becoming able to do it.