Sometimes when you speak to a friend, your words are not accepted.
Still, you can be motivated by your own words.
A ball cannot enter a stone wall, and therefore bounces back from it.
When your friend refuses to accept your words, they likewise are reflected back to you. You are therefore influenced by your own words.
These same words may have had no effect if you would have spoken them to yourself. But when you speak them to your friend and he is not influenced, they are reflected back to you. You are therefore motivated by them.
Source: Rabbi Nachman's Wisdom by Rabbi Nathan of Nemirov
Translated by Rabbi Ayreh Kaplan