We are constantly bombarded with many things in our environment. Our mind will filter out majority and give attention to those that are more important. For instance, few people would stop by to look at a flower grown at the side of a busy walkway.
When too many things happen and we need to process them, our mind become overwhelmed and would turn away from these stimuli.
Take for example that you are typing on a computer rushing some work, and the phone is ringing. Someone then steps into the office asking for direction (and it happens you are the only person there). Just three things that happen at around the same time could possibly make you lose focus.
This is environmental hypnosis and is a common phenomena in our daily life.