There is a simple explanation for it. Your body and mind, your entire system is trying to function on optimal levels, but it needs a period of rest and restoration to gather its forces back together.
Most of us are not spending enough time to let the body and the mind rest, which leads to the accumulation of unprocessed information and loss of some of it. At the same time, many functions in your body work in a way that they have a limit, so-called tolerance threshold. When this limit is reached, then your system shuts down, not being able to take in any more.
In other words, what gets overstimulated, gets resistant. This is true for many things in your body. You eat too much sugar – your insulin receptors get overstimulated and develop insulin resistance. Your body fat level is too high – leptin receptors develop fat resistance, which makes it difficult for us you reach satiety. Your senses get overstimulated, and they shut down, developing resistance to any incoming information.