Phrases that have marked your life

It was my tenth or eleventh birthday. I don't remember well. However, I remember this phrase very well, indelibly imprinted in my mind. I opened the presents and my grandfather (knowing that I was a bit selfish and disrespectful) said in my ear "There are two important things that you should never forget: the first is that the work you do, or that someone does for you, must be paid honestly. The second thing: you must always return a gift received with a gift from you because gifts do not make a sincere friendship but are the foundation of civil coexistence"