About
Carriers = Instant Win (also known as Mass Carriers = Instant Win) is, just like Zerg Rush, You Must Construct Additional Pylons, and In Ur Base, a meme originating from the 1998 RTS hit, Starcraft. The Carrier is the Protoss race's biggest, and most powerful unit.

Origin of Meme
Though the date is currently unknown, Carriers = Instant Win popped up on Gamefaqs. The logic behind the phrase, is that new players, not knowing how to play the game well, will expect that all they need to do is build the strongest unit, and lots of it, to win a game. The problem is, that large amounts of Carriers, though devastating, is not normally used by most better players, due to many other, faster attack styles, and it has been <a href:"http://starcraft2forum.org/forums/showthread.php?t=5525">debated how useful the tactic is.

On the topic of Instant win, says,

A term which originally became popular in the days of Starcraft. It was used to designate a particular strategy or attack which would guarantee victory for whomever was using it. It was often used in conjunction with the popular equation, "Mass Carriers = Instant Win". The strategy of mass-producing the largest aerial unit in the game and using it as the sole attack force remained popular, and later spread into Warcraft 3, where it gained the updated equation, "Mass Wyrms = Instant Win".
Mass Zealots = Instant Win!

When says,

Carriers = Instant Win is a catchphrase from the StarCraft board originally made as a mockery of "newbie" mentality, following the belief that building a large number of the most expensive top-tier units would create an unstoppable force. Of course, the actual application in game wouldn't turn out that way, but nonetheless it was common for newbies to go for mass carriers as their game-winning strategy.

Because of the satire aimed at newbies, the phrase was a common response to topics regarding supposed unbalanced gameplay elements. However, it soon became the default to any strategy discussion, and was designated as a fad. It later spread to other boards, including LUE, where it has achieved the most infamy.

Variations either include "Mass" at the start or omit it, and a variety of other "= Instant Win" or "= Win" phrases were derived from it. The fad also carried over to several other games, again using the most expensive top-tier units as a supposed "cookie cutter" to secure easy victory. For example, in Warcraft III the phrase "Mass Chimera = Instant Win" was used.

The Next Generation
When Starcraft 2 was announced, the usage of the term increased with more topics like This popped up.

And even a few YTMND's, like this one, and this one.