It is just a reminder that people are often going through difficult times that we are not aware of. It is why we are told,
(1 Corinthians 13:4 NAS77) Love is patient, love is kind, and is not jealous; love does not brag and is not arrogant,We do not know what struggle, loss or failure is dominating the thoughts and emotions of people we meet. It could be that the clerk in the store is not really surly, they may have just heard they have cancer. The guy cutting you off may actually be going to a fire.
As a follower of Jesus it is my responsibility to give the other guy the benefit of the doubt. It is why we are told to answer softly, go the extra mile, forgive and love our enemies.
homo unius libri