Here's a short piece on Spider-Man with a brief interview with John Romita Sr. Unfortunately, right off the bat, it repeats the following "fact"…
The editors of Marvel Comics thought so little of writer Stan Lee and artist Steve Ditko's creation in 1962, that they put the character's debut in the 15th issue "Amazing Fantasy," a comic set to be canceled.
First off, the "editors" of Marvel Comics at the time were one guy — Stan Lee, who most definitely believed Spider-Man could be a hit. The detractor was publisher Martin Goodman, who simply didn't think anyone would buy a comic book about spiders.
Actually, the way the legend is usually told is that Lee and Ditko knew Amazing Fantasy #15 would be the final issue so they figured they had nothing to lose by doing such a dangerously different character in it as a one-shot. But that account apparently isn't true, either. When they did the story in #15, they thought it was the first of many so they went ahead and did another Spider-Man story for Amazing Fantasy #16 and at least started on one for #17.
It was around then that Goodman received some uncommonly low sales figures on issues of Amazing Fantasy prior to the introduction of Spider-Man, back when it was called Amazing Adult Fantasy. He decided the book was such a loser that distributors wouldn't even bother to get later issues onto all the newsstands. Moreover, contracts then limited the number of comics he could publish so he had to cancel one to start another. He was not yet convinced that his new super-hero books were his best commercial prospect and still believed in his western titles. A year or two earlier, he'd cancelled Two-Gun Kid, then decided it was a mistake to have done so. Since then, he'd been looking for a slot on the schedule so he could resurrect it, especially since he had the artwork for an entire issue on the shelf, paid-for but unpublished. Add to that the fact that Goodman did not think the idea of a spider-themed hero was commercial and you have the makings of a boneheaded (but not fatal) error. He cancelled Spider-Man's comic after one issue to make room for the revival of Two-Gun Kid.
Fortunately for comic book history, he soon saw his mistake. Sales went up on that last issue of Amazing Fantasy, fan mail (then, a rarity) arrived, the other super-hero books were doing better and better, and Stan Lee was telling him the new hero deserved another shot. Goodman finally bowed to the inevitable and cancelled a romance comic to clear a spot for a full book of The Amazing Spider-Man. The leftover material, prepared for Amazing Fantasy #15 and #16 was incorporated into the first two issues of the new book.
That's actually how it happened. Don't believe the other version. (It also apparently isn't true that Jack Kirby was replaced as artist on Spider-Man by Ditko because Stan thought Kirby's version was too muscular. But I'll get into that some other time…)