"The law of probability" should lead you to no such belief. Instead, you should realize that the odds of breeding a particular dragon is EXACTLY the same each and every time you try it; that each attempt is an isolated event; that the number of attempts has absolutely no relevance and should not inform your expectations.
The laws of probability allow that no matter how high your chances are (and 6 times whatnot probably isn't close to high), it is still theoretically possible to try a million times and not get it. It's just as possible (although not as probable) to bag your ultra rare dragon on the very first try.
Now if you were drawing from a box with a finite number of jellybeans, your odds of pulling out the single black jellybean would increase with every non-black jellybean you got. But you're not drawing from a finite pool here; you are tapping into an infinite supply of dragons, so you could hypothetically breed Fires forever. You really should take a break and go grab a snack though. Jellybeans maybe? Red?