This is the most important thing.
I believe it should be because music makes you feel something that you involve yourself with it. You should write and practise music guided by your own feelings. If somebody gives you an opinion, it should still be ultimately your decision. In some sense, it might even seem selfish to write music for yourself that satisfies your desires, but you see, if you don't feel something yourself when you work on your music, then how do you know what your audience is supposed to feel? Think about that. Find words to describe it to yourself.
To be professional, it may be necessary to craft a music well, or to perform pieces you might not always like. Ultimately, though, you should be searching for something you yourself feel.
Nobody can explain quite why there's a feeling in one song or piece, but not in another similar one, but you just have to accept that there is and stay in touch with it, recognising it when it's there. Some people will say that "it's all a matter of individual taste and who's to say what's good and what's bad?", but that's a load of bollocks because the music that has that feeling is almost universally recognised by the public who are unbiased and only grabbed by what they are grabbed by and most of it is forgotten as soon as it is off the air.
You are unlikely to "make the bigtime" even with talent, so don't be sucked in by all the loopy idiots hyping up nonsense. There are millions of them. You will only be rewarded when there is a feeling flowing through the music. It's even more important when you do have a record contract because there is so much corruption in the music industry that if the public don't feel something, you won't break even and may end up owing The Man millions in illegal payola etc. If a money-man who can't play tells you what to do, remember that if he leads you astray, he will keep his job and you will not.
The thing that confuses the issue is the abundance of formulaic "pop" that always seems to be in the charts making you think that you just do it by the numbers and the cash pours out of a jackpot machine. There are many tricks the money men pull to keep it looking that way, the least of which is buying their own records to fake the sales figures. In reality the record companies have always lost money on most acts. If you don't believe me, just look at the next video with hot girls jiggling and ask yourself why anybody would buy a CD of this for thirty bucks when the cover is far too small to ogle. You'd be more likely to buy a poster or something. You wouldn't listen to it, would you?