When rain falls on vegetation, especially mature plants, you probably won’t notice any immediate improvement.  It takes time for the rain to have a visible effect.

It’s no different when giving someone advice.  You do your best to try to guide that person, but you don’t see an immediate change.  But don’t stop trying to help him or her.  Eventually you should notice an improvement.  Even if you don’t, you fulfilled a noble purpose by making the effort.