...Yes a lot of people tend to not be honest with themselves at times and we could all be more disciplined. Discipline goes a long way in life.
May I ask what level you teach at? Because I feel this is more a problem with younger students who aren't as interested in music, with students who are more serious it wouldn't be a problem.
.....Discipline, and in particular the habit of self-discipline, comes close to being everything, no matter what the musical goals, and of course these vary greatly with the individual.
And its importance carries over into old age, at which stage many musicians seem lamentably to stand still. At sixty-nine, I couldn't bear that; I have to work at new ideas every day else I would just as soon labour in the garden. My teacher had the opposite problem with me. I used to work myself into the ground each week to do just a few of the things his gifts allowed him to do at once. "I understand how difficult it must be for you Ted," he kept on saying, "but you'll get it one day. Might take you about ten years but you will get it if you work, I can tell." He was right. Practically exactly at the ten year mark, things started to happen. Sad he didn't live to see most of it.So your pupils will certainly reap the rewards, musical and otherwise, in the distant future, of any discipline you can impart, even if you might not be around to see it.
Dicipline is not actually necessary though... It's something that comes with personality and/or is learned at early age. I've never had any. Even as a child no-one could force me to do anything, I was stubborn as a mule.
Now as an adult I have had to create some daily routines and tricks to lure me into practicing on the days when I am less inclined, but never am I able to force myself and sometimes I just don't these days. What boosts me to practice is knowing my playing sucks and believing that I might be able to do something about it with regular intelligent practice. If I thought I was any good I probably wouldn't bother...