Just came across this today so I figured I better post it...
According to Or HaChaim on Genesis 30:2
ויחר אף יעקב
Jacob became agitated...
ודברי הצדיקים אפילו בסדר זה יעשו רושם
the words of the righteous even when okay [conditionally] make an impression.
I also found a footnote in the Artscroll Or HaChaim that references this quote with Sefer HaChinuch, Mitzvah 231
Even thought we do not have the power to know in which way a curse impacts upon the one cursed, and with what power within speech there is to bring [that impact] upon him, we know more generally that people are concerned about curses - whether Israel or other nations - and say that curses of people, and even curses of commoners, have an impact on the one cursed and attaches malediction and distress to him. And since we know this thing from the mouth of the creatures, we will say that it is from the roots of the commandment that God prevented us from injuring others with our mouths, [just] like he prevented us from injuring them with action.