I absolutely agree Mclesh, the problem is, when you're starting out you don't know what 'good' is.
On my current manuscript, I sent out about 20 queries with a prologue I knew was weaker than Chapter 1, but I thought would stand up. A few requests, but only from 'query only' agents.
Scrapped prologue. Re-wrote everything. Another 40 queries. A few requests, but nothing to write home about.
Focused on the MC, his feelings and character development. Gave him a real, flawed, understandable nature. Re-wrote Chapter 1 three or four times. Went through a couple of beta readers.
Another 40 queries out, this time lots of bites, one of which turned into an offer (which I have to sign and take to a courier on Monday).
The funny thing is, while the agent was going over it I noticed a rather large flaw in the plot which could be easily fixed by adding a new chapter, re-writing a few dozen lines in the rest of the book and deleting a half-chapter that was fine, but not great. So, it was 'good enough' but I'm still finding ways to make it better.
There's a story told about Tolstoy, I don't know if it's true or not, but some claim that when he died they found reams of revisions to War and Peace, dating right up to the days before his death, 41 years after the book was published.
Always make an effort to improve your skills as an author. Always look for ways to improve your manuscripts. Work hard and learn well. I think those are the 'secrets' to making it in this crazy industry.