Cortisol is a hormone produced by your adrenal glands. It increases glucose in the bloodstream and curbs functions that would be nonessential in a flight or fight situation. Evolutionarily this makes sense, but our modern world creates stressors that usually don't involve running from a tiger. Cortisol release is triggered by any stressful situation, regardless of whether or not you could truly label it as fight or flight.
Hence the button, to remind you that you can't control your hormones, so cut yourself some slack!
This listing is for ONE 2.25" round button. It's a pin back button, with the design on the front.