When we think of all the different neurotransmitters (dopamine, serotonin, etc) we sometimes forget that the vast majority of neurons are producing either excit

When we think of all the different neurotransmitters (dopamine, serotonin, etc) we sometimes forget that the vast majority of neurons are producing either excitatory outputs (via glutamate) or inhibitory outputs (via GABA). The other neurotransmitters are modulators of this basic phenomena of excitation/inhibition. The brain has a tightly balanced feedback loop between excitation and inhibition. Too much excitation and the brain gets a seizure (positive feedback). Too little, and you black out. TBH, it's quite a good example of the principle of balance in the concept of Yin-Yang.