Katherine Kurtz sold her first trilogy (all 3 books) to Del Rey in the 70's -- all by herself. It was the beginning of a long and still-going-strong career in the fantasy genre. Obviously times have changed since the 70's. But success without an agent is certainly something that CAN be accomplished by the well-informed, yes?
You don't have to have an agent.
If you capture Osama bin Laden, I guarantee you that you can have a book deal without an agent.
If you win the Nobel Peace Prize cause you settled the conflict in the mid East..same deal.
If you are trying to be published in the less esoteric realms, like genre fiction, or memoir, or prescriptive non fiction, you still don't absolutely have to have an agent. Most major publishers won't look at unsolicited work, so you're limiting your access to publishers with big money, but ok.
You can submit your work to medium size houses and small presses; no problemo.
Here are a couple things to ask yourself:
Do you know what an escalator clause is?
Do you know the difference between translation rights and foreign rights?
What happens if the editor who acquired your book quits? or worse..is fired?
Who gets your rights if the publisher goes bankrupt?
Do you get paid for books that are sitting in a distributor’s warehouse when the distributor goes bankrupt and his assets are sold off for pennies on the dollar?
What happens when the publisher wants the advance back because they changed their minds about publishing your tome?
Smart people know they don't know it all. Really smart people recognizeit's not a limitation to acknowledge gaps in knowledge. Really really smart people surround themselves with people who know a lot about specific things.
Yes you can do this on your own. The better question is, why would you?