TAC-tIC

We say tick-tock and not tock-tick, we say ping-pong and not pong-ping, and we say tic-tac instead of tac-tic. There are countless more examples, from spic-and-span to flim-flam to jibber-jabber to King Kong. Surprisingly, there's a reason why the reverse of these common phrases sounds off to our ears. In linguistics, it's known as the rule of ablaut reduplication. In any grouping of two to three words with the corresponding vowels, our brains naturally find it easiest to think in terms of I, A, and then O. That's why "big bad wolf" is said that way instead of following the more grammatically correct "bad big wolf" (as it's customary to put opinion adjectives in front of size adjectives), and that's why all these other variations exist. It's our own minds tricking us into what's "right"; just another quirk of the human race.