Everything we say and do does not happens in a random vacuum, because we think before we speak.
Thoughts are real – they occupy mental real estate. Every thought has a “heart” – the intention of that thought. God looks at this ‘heart’ (Jeremiah 17:10) to give to each man according to his ways and according the results of his deeds.
Essentially it is naive for us to think that any thought we accommodate is harmless.
No thought is harmless, to elaborate a bit, you can’t have a negative thought about someone and smile at them sweetly and think you real thoughts are not going to be transmitted.
” And the LORD said, Behold, the people is one, and they have all one language; and this they begin to do: and now nothing will be restrained from them, which they have imagined to do.” Genesis 11:6
The science of this scripture is that as we are thinking we are physically building substance, and whatever is substance in your brain you will act upon, so if you watch someone eat your favourite meal, and you were hungry, the same areas in your brain will light up as the person eating the meal.
God has designed us to be entangled in each others life, what it means is that you thought are impacting you Spirit,Soul and body, the people in your immediate environment and also of  people that are 10000 miles away, if their is a toxic thought of bitterness or unforgiveness imbedded in your mind against someone 10000 miles away, you are impacting your life and theirs no matter how far away they are , there is no limitation of Space time in the thought dimension. Quantum physics actually explain this in terms of the theory of entanglement which means we are all connected to each

Quantum physics actually explain this in terms of the theory of entanglement which means we are all connected to each others lives. So we feel each others emotions. You can’t hide an attitude because of the design of the brain.  God has designed us with mirror neuros in our brain, only God and you know your thought.
When you are around some who is negative, it makes you feel horrible, when you are around someone that is joyful you feel great because our attitude rub off on each other, no thought is harmless. Every thought you build generates electron magnetic energy and produces a state of mind, and it is part of non-verbal communication, because the attitude comes through. We have all sort of structures in our brain that help us reflect each others emotions, for example the vagus nerve,insula and mirror nerve cells of our brain helps us to play, cry, work ..together.
Every single cell in our body is impacted by a negative thought, no thought is harmless, no attitude is hidden, the thought will come out even when not spoken. Aggressive thoughts about others reduces the healing property of the body considerablely.
Finally it is important we are aware that stuff does pass through the generations, the decision that your great great grand parents made are in your head. When we are not using our minds (intellect, will and emotions) to listen to what the Holy Spirit lays down in the depths of our spirit, then we will be listening to the lies of the enemy . Whatever we listen to, we will think about and whatever we think about grows into a physical thought with its’ ‘heart’ being reflected as our attitude. People pick up on our attitudes – the intent of the thought – not the detail of the thought. The brain is designed with various structures that facilitate this to happen….reflecting our ‘hearts’ is how God designed us.