Our words are like a mirror that give others peeks into our hearts. If the mirror is unclean, it distorts whatever it reflects. Similarly, if our words are thoughtless, they can give others a distorted picture of our heart. We may deeply care for others, but if we are careless in the words we use with them, they will misunderstand us. And the responsibility for that misunderstanding will fall on us, not them.
When we are stressed, we may vent ourselves by speaking harshly to anyone who just happens to come our way. Or when we are annoyed with someone, we may burst out by speaking cutting words that are way out of proportion with their mistake, even if we are correct in assuming that the mistake is theirs. Our inconsiderate words may make them feel that we are inimical to them, thereby scarring or shattering their hearts and disrupting, even destroying, our relationship.
No matter how busy we are, if we want to see our reflection, we take the few moments necessary to clean the mirror. Similarly, no matter how pressured we may be, we need to take the time necessary to clear our mind of the dust of impulsive emotions and think carefully about the words we use to express ourselves. The Bhagavad-gita (17.15) urges us to discipline our speech by choosing words that are non-agitating. The same verse urges us to speak truthfully, meaning that we don't have to pamper others with counterfactual flattery. But we do need to temper our emotions by using words that reflect our care. Such words increase the probability that they will hear us out objectively, not defensively or aggressively, thereby facilitating resolution and reconciliation.
When we learn to use words thoughtfully, our words won't unintentionally drive others away, but will draw them closer to us.

Unthinking words reflect an uncaring heart