Our body moves as the brain orders. If the brain loses its function, other parts of the body cannot play their roles properly, so the brain is the most important part of the body. The brain receives a great quantity of blood, which is fuel for the body, because it performs that much important function.
However, the brain has a weak point. When you say something, your brain does not know whom your words refer to. If you say negative words to others, the brain does not know if the words are applied to yourself or to someone else, so it orders to release stress-producing hormones. On the contrary, if you say positive words to others, the brain recognizes that they are applied to yourself and so releases happy hormones in your body.
Therefore, we should speak only positive and optimistic words even for our own sake. If we say positive and optimistic words, we can benefit ourselves and listeners as well. So, the fact that the brain does not distinguish to whom you speak can be a blessing, not a weak point.