Listening is the most ephemeral of skills. We as instrumentalists regularly strive to correct and improve techniques of the left and right hand. Etudes, scales, studies, exercises, warm-ups, runs and licks are all practiced to refine the physical demands of our instrument.
I have mentioned on another page of this website, that " Music is the Art of the Ears Not of the Fingers". The end result of all of our practice need ultimately to be scrutinized by our careful listening. Perfectly elegant and fluid ergonomics mean little if the audio results are not noticeable.
Sometimes when I am working with a student, I will inquire, "Can you hear that?", "that" being either pitch, tone quality, tone production, nuance of a phrase, articulation, etc......
Surprisingly, I find students not being able to scrutinize with their ears as carefully as necessary. This will lead me to question the student about their listening habits in daily life. Does the student walk around with ear buds in while consuming music walking around? Does the student have music playing in the car? Does the student listen to music, movies, TV during most resting moments?
This generally tends to be the case. What happens in my opinion is that the modern young person experiences " Listening Fatigue". If your ears are subjected to passive listening for hours on end, the sensitivity of your ears and the quality of your listening will be affected negatively. This is true of any physical activity where there is mindless constant actively affecting physical well-being.
As a result, I have my students then participate in a " Listening Fast". They are not to listen to any music or any other electronically generated sound unless they devote a specific amount of time just to do that. For instance, if they want to hear a song or piece a music, they have to sit in a chair, and focus totally on that listening experience. No email checking, chatting with friends, texting, gaming, etc. They only listen. They do though continue their normal practice schedule and routine which I assume they will do with utmost care.
I have found that a week of a dedicated listening fast, improves listening capabilities tremendously. The point really is to appreciate one's hearing and respect the wear and tear that constant exposure to sound can drain your hearing capabilities. Good listening is a skill and the brain needs time to recover so that the sensitive parts of the listening apparatus have time to heal.