Most of the people I've met in the writing profession are wonderful: intelligent, helpful and fun to be around. But there's a minority who amuse and sometimes irritate: those who believe they wrote the only book(s) that will ever matter.
Most of us recognize that we're in a business where tastes vary. Along with those who love my book, I've met people who damned it with faint praise or dismissed it altogether. One woman told me recently that it was too much work to read a historical piece. A writer has to recognize that not everyone in the world will like her style. We'd all love to be that author that everyone gushes over, but even the best have their detractors.
So why do some authors insist on believing that they are the Second Coming of Charles Dickens or Jane Austen or whoever? On panels at workshops, some authors don't get the idea that it isn't their own personal show, that they're supposed to share the stage. I've seen authors who actually never got to speak on their panel because some well-intentioned but bone-headed author let his ego get in the way of the things he should have learned in kindergarten.
I've been imprisoned by authors who need to impress me: one who read to me from his work at great length while I was supposed to be signing books, many who cornered me to spout their own praises until I just wanted to cover my ears and do the "nah-nah-nah-nah" thing. I saw a fellow author's book signing ruined by a wanna-be who monopolized the entire two hours telling him about his great unpublished novel. (Yes, we tried to save him, but it didn't work.)
I've met authors who tell me that I MUST read their book. One told me I had to read it because he guaranteed I would laugh out loud, several times (I didn't). One said everyone in Michigan should read his work because it was of interest (to a whole state?).
The joke in the business is BSP, blatant self-promotion, but there is a limit. Yes, you have to promote, because these days nobody does it for you. Yes, it will sometimes be blatant. You have to learn to be like the salespeople at Macy's, able to make subtle suggestions that lead a potential customer into becoming an actual one.
But you don't have to brag. You don't want to shove others out of the way. And you can NOT take the approach that your work is better than someone else's. Tastes vary, and only the reader can decide that.