There's nothing wrong with writing about what you know (indeed, a trait more people should exercise!) or writing music for a particular segment of society (twelve year olds for example) but when they play identical song after song after song and then repeat it over and over and over, so all you hear all day (if you work somewhere that plays only a certain radio station day in and day out) is whiny teenager girl lamenting her lovelorn anguish and how it isn't ever going to get any better at the ripe old age of thirteen, well, you understand where the term 'postal' might come from, even the most gentle and docile of temperaments must have their breaking point! She had not (and happily so) suffered much at that age and her music shows it, but why someone chose to make her famous and play her songs everywhere for the rest of eternity is beyond me, unless those children's book producers have now invaded the music scene, disturbing thought indeed! True art, of whatever form or format or genre, comes from the heart, and the more that heart has seen, loved, grieved, and suffered, the more moving is that art. Albeit suffering does not equate with talent (or perhaps taste?) as Picasso obviously suffered greatly, and though famous and renowned, I still feel like most of his masterpieces were filched from a seven year old's art case, but that's just me, perhaps I have no eye for that sort of art any more than I have an ear for music made for teenie boppers.
I've observed this in my own case, when writing (for good or ill), I always feel like my muse waxes hottest when I'm struggling with something significant, either present or past. And then there are those days that are bright and sunny and happy and I really can't write a coherent sentence, let alone a decent composition of any sort. Is it that those who have suffered have a greater understanding of our humanity, mortality, and the greater things beyond, or is it that they are driven to create as an outlet for their grief? Perhaps it is some combination of the two? If only we could find someone to write a nice little thesis on this theory, but as doctoral theses are far from works of art, no matter your discipline, that might be disaster indeed!