Lots of sense in that article, but there's still no guarantee that querying 100 agents will get you favourable results. I queried 156 agents and publishers with an open submission window in the first seven months of 2015. I've received 53 form letter rejections and 5 personalised refusals which offered guarded praise and some useful advice.
What exasperated me the most about querying was the bewildering variety of stipulations that agents make for the form of a submission. Some want the first three chapters, others the first 5,000 words, while one requested what I thought to be the most typical chapter of my novel. The latter struck me as quite sensible compared to those who were making judgements of the opening of a story, looking to be immediately grabbed by the throat with a potentially gimmicky bit of sensationalism. If you take into account the advice that writing is rejected in the first five pages, or even the first five sentences, then any submission comes under heavy fire straight away. I strongly recommend
Noah Lukeman's The First Five Pages: A Writer's Guide To Staying Out of the Rejection Pile to anyone polishing their manuscript.
It became plain to me that the publishing industry is stuck in past times, with book companies and agencies operating as individual fiefdoms—all demanding different things of their serfs, the unpublished writers waving their manuscripts vainly at them. There's certainly no standardised way of making a query, no shared clearing house where potential novels are sent to the best book company. Publishing is a cutthroat business, and there's a lot of collateral damage—us!
The best thing about making multiple submissions is that it helped me to hone my query, to become much more selective in who I approached and to view rejections as adding another layer to my rhinoceros hide. When I read that JK Rowling was rejected by a dozen publishers I smile grimly—a whole
dozen—what a baby!
I have the feeling that one has to keep knocking on doors in the hope that by being persistent (irritating) someone will finally look at your work properly. It's almost like an initiation rite, whereby agents sluggishly respond to those that they've swatted away dozens of times before.