When your phone is in your pocket, there are two possible states: it is

When your phone is in your pocket, there are two possible states：it is either vibrating or not.
       Meanwhile, you also have two possible states of mind：the judgment that the phone is vibrating, or that it isn’t. Ideally, you match the four states, correctly. However, sometimes your brain decides that the consequences of missing a call are more serious than a “false alarm”. Therefore, you become more sensitive to vibrations so that you don’t miss anything.
       This is just like the fire alarm in your home—it can be annoying when it goes off in response to just a tiny bit of smoke. But that’s a small price to pay compared to a fire really breaking out because the alarm fails to alert you.