Although your brain is just three pounds of soft, gooshy tofu-like tissue–it has about 1.1 trillion cells.
There are 100 billion neurons in your brain, averaging about 5,000 connections each–called synapses– like having 500 trillion microprocessors wired together in a vast network.
When a neuron fires, that excites or inhibits its receiving neurons. Basically, the sum of all the signals a neuron receives determines whether it will fire–sort of like the dominant message from a crowd of people all shouting “go!” or “stop!”
Adding up all possible combinations of 100 billion neurons firing or not, the number of potential states of your neural network is at least 10 to the millionth power: one followed by one million zeros. (There are "just" 10 to the 80th power atoms in the entire universe.)
Neurons typically fire 5-50 times a second, with millions and even billions of them pulsing together.
In the half second it takes you to clap your hands, billions of synapses have activated in your brain.
Most brain activity is lightning fast and forever outside of awareness. The slower stuff that we call thoughts and feelings is just the observable tip of an iceberg of lightning quick electrical, chemical - and possibly quantum - activities.
More than learning how to use tools, more than adapting to moving out of the forest into the grasslands of Africa, it was learning how to love and live with each other that drove recent human evolution.
Even though your brain is just 2-3% of your weight, it uses about 20-25% of the oxygen and glucose circulating in your blood.