One night does not a season make. But as I’ve stated before, the real unknown regarding “The X Factor” will be what effect having another competition show on in the fall has on the winter-spring run of “American Idol.”

Fox has understandably downplayed the idea that one show might cannibalize audience from the other. But the 25% drop in preliminary ratings for “Idol’s” return certainly raise the issue. And while Fox can say Judging_NJ_Day1_0217part of the problem is a proliferation of such shows across the dial, only Fox is responsible for “X Factor,” which looks more like “Idol” than any of the others.

Obviously, the producers of “Idol” recognized this threat, which explains the legal wrangling over the program’s launch in the U.S.

Of course, even with a significant decline “Idol” remains a juggernaut. But nothing stays airborne forever. And if “X Factor” hastens “Idol’s” descent back to the ratings orbit of mere mortals, Fox might wind up regretting the day it agreed to “X Factor” after resisting the temptation to do two editions of “Idol” a season.

As they famously said in “Wall Street,” “Greed is good.” But it can also have unintended consequences. And while we’ll never know exactly what the impact of “X Factor” was on “Idol,” by May, there ought to be enough evidence for a pretty good accounting of what Fox gained — and lost — in the bargain.