This is Locard's exchange principle, from which evolved forensic science. In that context, it is understood that any person at the scene of a crime will have brought something with them and will take something away with them. Thus if there is a trace of a certain person in an incriminating context, it builds the case that they were participating in an incriminating act.
But it's not just criminals whose presence leaves a mark. The principle applies to all of us, and I'm not just talking about physical traces. Every encounter that we have, whether it's in person, on the phone or over the internet, has an impact at the other end of the interaction.
And here's where I think it gets really interesting: when your thoughts, words and feelings intersect with the thoughts, words and feelings of another person, the thoughts, words and feelings of each person in the interaction are set off in a different direction than they were travelling before.
Like the classic executive desk toy, when one of the spheres hits the next, its energy and direction is transferred. That sphere in turn passes its energy to the next along the chain, and so on.
There's probably much more subtlety here. But in basic terms, it's frankly an amazing thing that we can be given such responsibility of influencing the direction of each other's intimate thoughts.
A similar concept lies behind the communication model known as the "Betari Box", which recognises that my attitude affects my behaviour, which in turn affects your attitude and thus your behaviour. And so the cycle goes round, for better or worse.
Once we recognise the phenomenon, the question is how we will use it. Our positive thoughts towards a situation or person will leak out of us. Just think what positive new thinking your interaction could spark for the other person, whether it's a dramatic 180º shift (usually it isn't), or variance by a few degrees towards an interesting destination.
We have more influence than we think, and it all starts with our trains of thought.
