Discipline is never an end in itself, only a means to an end.
Music never goes away. It is always available, but we're not always available for music.
But above that, most mature adults can hold their attention on something for 45 minutes, whether they like it or not. But above that requires training.
Purely by hard work, one can become an artist.
What we hear is the quality of our listening.
According to USA today, the average length of an attention span of a man in America is 23 minutes.