On my way to work I was reading today about the Reticular Activating System. The May 1957 issue of Scientific American described this location in the brain that serves as the gateway to our conscious awareness.
In essence, the Reticular Activating System permits stimuli to enter our consciousness that passes our predetermined criteria. We may be able to fall asleep in noisy environments when the noise is not important to us or wake up when extraordinary events cannot be ignored. The examples were waking with the sound of a crying baby or falling asleep with music playing.
As I considered this phenomenon I thought about how we focus on those things that are important to us.