How to keep the interests going

Just discussed with a parent about student losing interest in violin. I took some time to think about it. Well, interests come and go. The younger the child, the more fleeting the interest. We can see that for young children to have a sustained interest in certain activity, they are either naturally born with it (i.e. "hard-wired" that way), or the interest developed through constant exposure. Some would include constant exposure even during pregancy time.
Learning a musical instrument takes more than interest, and more than talent. They amount to only about 10%. The other 90% are hardwork. Oops! It's too hard. So we need motivation to go along. Unfortunately, motivation is short-lived. So how do we get the "hard work" done?
For one thing, we can keep motivation coming. This can come from teacher, parent, and constant exposure.
As a violin teacher, I only see my student once a week, at most twice. Parents generally would not fork out astronomical fee to hire a violin teacher every day of the week. Oh they would do that for subjects like Maths, Science, etc. at the drop of a hat, but violin? Not unless they wish their child to be a world-standard virtuoso.
So here is the catch. The parents have to make 6/7 of the motivation, with the teacher doing 1/7. Well, maybe 3/7 of the motivation, the other 3/7 would be to listen to really nice violin music, orchestra music, and take part in musical activities, like orchestra rehearsal, mix around with other violin students, compare and contrast notes, etc.
That way, the 90% hard work would not feel so hard. And it can develop the strength of determination, the will to overcome challenges, and be a better person to face the challenges of life in general.