Everything we say and do in life has consequences. Just like throwing a stone into a pond sends ripples across the water.
We are free to say and do as we choose but the consequences of our words and actions are our responsibility.
How many times have hasty words been spoken making a wedge between once loving friends or spouses?
Sometimes we think something bad about a person and in anger or when emotions are high, we make those thoughts vocal. If we could have waited a little, these negative thoughts may well have been replaced with more kindly ones.
To speak or act while in a state of anger is really a mistake. It is a good idea to hold your tongue and wait until the next day. If the same level of emotions is present, then speak out, but most chances are you will have forgotten why you were angry.
[The good deed and the evil deed cannot be equal. Repel (the evil) with one which is better (that is, Allah directed the believers to be patient at the time of anger, and to excuse those who treat them badly), then verily he, between whom and you there was enmity, (will become) as though he was a close friend.] [Sura 41 Fussilat, Verse 34]