Usually when we get a sensory input our brain couples it to the memory bank and this is how we perceive the world around us. If we see a house we have seen before most of the data actually comes from the memory bank and only a fraction of the perception from the sensory input (the eyes in this case). What usually happens next is that this input starts a chain reaction in the memory bank through the couplings with the memory that was triggered by the sensory input. If we for example recognize a certain smell we couple to the situation where we recognize the smell from, then we start to think about the people that were there or something else coupled to that memory. This is an internal process in your memory bank and draws away attention and actually makes you perceive less of the world around you. To stay focused is to avoid unconscious chain reactions in you memory bank, without this background noise you will feel your sensory inputs much clearer. In fact your update frequency will rise and you will actually have more time at your disposal and your actions will therefore require less effort.
An analogy to this is pushing a wheel-chart with a square wheel on uneven ground. The flat surfaces on the "wheel" corresponds to the time spent in the memory bank between the sensory inputs (the input from the world around you). When you learn to stop the chain reaction in you memory, and turn your focus to the present, your wheel will become more and more round. When there is no other activity in the memory bank other than the registration of input you will be in a flow, with a different perception about time and your actions will more efficient and require less effort.
