Is it a sin to psychologically harm someone by directing harsh and demeaning words at them with the intention of pushing them away, especially if the speaker knows in advance the severe impact their words will have on the other party, and could have used a better approach to avoid causing harm?

Harming a Muslim through insults, curses, backbiting, or slander is a sin and is impermissible, based on the Almighty's saying: "And those who harm believing men and believing women for [something] other than what they have earned have certainly borne a slander and a manifest sin." As for mere harshness and sternness in speaking the truth without aggression, there is no sin in it, even though gentleness, leniency, and good speech are more perfect and better, based on the Almighty's saying: "And tell My servants to say that which is best," and the Prophet, peace and blessings be upon him, said: "Indeed, gentleness is not found in anything but it adorns it, and it is not removed from anything but it disgraces it," and "Indeed, Allah is gentle and loves gentleness, and He gives for gentleness what He does not give for harshness."