Generally speaking, the key is sensory awareness. Humans have kind of evolved to fit into their environment by filtering out information they don't need. If you actually look at the amount of data coming in through all your senses, there's something like 100 million bits of information coming in every second through your visual system and another 10 million bits coming through your auditory system and another one million bits coming through your tactile system.
We are at any given time, absorbing hundreds of millions of bits of data per second through our senses. We can manage this, because our conscious stream is only aware of a very tiny fraction of that sensory input, maybe a few hundred bits per second. Most of our intelligence is really a filtering process, determining which of those bits are most relevant at any instant. Our sensory awareness is really much higher than we perceive. I knew that I knew more than I thought I knew.