When we gossip about others it may feel that we are not doing any real harm. After all, what we say will most likely never be heard by the person we are talking about. So what's the harm?

When we engage in idle gossip about others, we waste our time and energy as well as the time and energy of those who are listening to us.  If we were saying good things about the person, we would be praising them not gossiping about them, so the likelihood is that we are saying something unfavorable. Even if what we say is just not particularly kind, even an unkind thought is negative and plants another negative seed, as we commit another negative karma.

Also when we gossip, we don't have any sense of fulfillment.  We didn't accomplish anything, and worse, we lost sight of our aspiration to awaken and help others awaken.

Finally, just as we view those who gossip as untrustworthy, our engaging in gossip deems us untrustworthy in the eyes of others.  So good people will pull back from talking to us and, eventually, only those who do not value integrity will want to spend time with us.