In plain words
When the thought of doing harm to others arises in us, those thoughts may do others some harm, more or less. They do. But these thoughts do not stop there. However much harm our thoughts do to others, they themselves come back and do us a hundred times as much. We must recognise just this truth, just this secret that lies in our thought. However much we hurt others, those thoughts come back and hurt us many times over. That is why we must recognise the truth that bad thoughts hurt not only others but us as well. When a venomous creature bites both the one who touched it and the one who reared it, poison enters the one who reared it too, not nectar. So bad thoughts cannot fail to hurt anyone at all. That is their nature. You have heard of it in the Mahābhārata. Through bad thoughts the Kauravas developed many kinds of thoughts, to torment the Pāṇḍavas, to do the Pāṇḍavas harm. These thoughts tormented the Pāṇḍavas to some extent. But far more than that, they turned back and tormented the Kauravas themselves. So when our thoughts are bad thoughts, they do more harm to us than to others. If they are good thoughts, they bring some good to others, to oneself and to the people around as well. So the moment thoughts arise, we must enquire into their good and bad. Do these thoughts sustain my humanness or destroy it? Do they increase my fame and honour, or do they bring me to ruin? Enquiring in this way whether it will do you good or harm, if it does harm you must try at once to drive those thoughts away. What is the way to drive those bad thoughts away? There is no other way to drive these bad thoughts away. Bad thoughts go away only when we develop good thoughts. When there is a bad smell all around, what is the way to remove that smell? We cannot remove the smell at once. We can fill in a fragrance, an incense stick or sāmbrāṇi or some other kind, and in that way see that the bad smell does not reach us. In the same way, when we develop thoughts of Satya against the bad thoughts that arise in us, these bad thoughts go away easily.
In every matter, the moment a thought arises we must enquire. We must enquire what this thought's future and effect will be like. Sometimes there is also a chance that someone else will sense our thoughts.