I've never pitched a book before (because I'm a wuuuuuusssssss with multiple trunked manuscripts *ahem*) but I HAVE done cold sales. The kind of cold sales where you flag someone down in a mall and try get them to sponsor children. The kind where you knock on doors and try sell you different television/internet/phone packages. Real... cold pitching... and let me tell you, that is punctuated with rejection. A TON of rejection.
In the sorts of cold sales I've done, your goal is to be hitting around a 1/10 conversion rate. That means 1/10 people you have a decent conversation with should buy the product. This should give you a good perspective of what a mall salesperson is expecting to deal with–not "1/10 people", because some people go out of their way to not look at you, pretend to be on their phone, slam the door in your face, pretend to not speak English–that's not a good contact. If you're not making those numbers, which are statistically pretty likely to pan out, even if you end up getting them in weird clumps, then you adjust the product or your pitch.
So, if you got 1/6 agents to request your book, you're doing, statistically, great! And this is how you cope with it. It's not your fault that those 9/10 people say no, they're having a bad day, they have a ton of the genre, they just bought a book with the same kind of theme and don't want two merman books, it's just not what the market needs right now. If those 1/10 say no, that's indication of a problem. Say you get 30 no's in a row, then maybe your book or your pitch needs a look. If you get 3-6 requests for fulls in there, then your pitch worked as intended, because closing the deal in this case is just trying to get a request for more. The second part of the sale comes with your work. If 1/10 agents who requested your full agree to represent you, statistically, that would be average for sales–because now your book is serving as the pitch. If you got more offers, then your product was great. If you don't get any offers for representation, then it's your book that needs the revising.
And you console yourself by saying, well, it was the stats. 9/10 agents don't want your novel because of reasons you can't control, it really DOESN'T suit their needs at this time, and whatever, you started writing because you enjoy writing, not because of the money and success and fame.
And then you move on and do it again.
And again.
And again.
This is the part that breaks potential salespeople. I've seen GOOD salespeople quit after a few weeks because the slog just isn't for them. Sales is hard, and selling a book is a multi-tiered sales process in which you have to secure representation (first by getting a request for chapters/pages/fulls, and then by convincing them with the actual reading) and then allow them to sell your product to a publishing house...
Selling a book is hard.
You must let the rejection bounce off of you. It is not personal. It is only the numbers. The numbers working against you, statistically making it impossible for everyone to be happy with your novel fitting into their business plan. You can only win by papering the inboxes of potential agents relentlessly, modifying appropriately if you notice a lack of response. Statistically, someone will buy it eventually... and if not, you can always self-publish, or fuel the agitation of waiting for the inevitable punch to the gut of rejection by writing another novel to spread across the desks of agents.
Good luck, and I think with a 1/6, you're going to be just fine.