Yeah, there's the getting too comfortable with it at the one end, and getting too uNcomfortable with your music at the other end. Neither is a good place to be, imo. If you get too attached with the music, you risk being too protective and loose opportunities as a consequence, and if you get too unattached to it, you might loose your drive and motivation to make music at all. It can be hard to find that balance, for sure. I think the unattachment part applies not so much when developing your music, as to when you have it signed and are asked to make changes by a library or music supervisor.
But once you find the genres you enjoy doing, and produce a lot of it, you just want to get it out there to work for you. So if you stick to producing new stuff continuously, it will most likely balance itself out without having to think about it too much. The problem with attachment are more likely to come if you produce relatively little music. Then you want to say everything in one piece at the time, which really can block you out. Unattachment can be a problem for learning too, though, if you just do what others tell you, and don't finetune your own tastes and sensibilities to your goals and targets. And who can honestly say they are unattached to their music, if they have developed great ideas, executed them well, and made it effective. In those situations you are supposed to be attatched to your music, it's a good thing, be proud. But for pastiche cues you just have churned out in three hrs due to the opportunity to a quick placement in a reality show, attachment seems unappropriate due to the work you have put into it, due to the nature of that type of music and due to it being produced for a particular use. Full songs 3mins+ seems to be more involved and more difficult to handle in terms of being unattached to it, allthough depending on the target.
So, no complex formula covers all, maybe other than write, submit, forget, repeat. The answers seem to arrive with the practice, and you have to contain different mindsets for different types of work. But like JJ Cale and Eric Clapton sings in It's Easy, "you'll be big, if you don't quit".
https://www.youtube.com/watch?v=0kxk11D-mpY
... or, however that saying goes. 