Why does “His to lose” mean “He will (most) likely win?

Romney is currently the frontrunner for the GOP campaign, if we ignore Cain for the moment (who has other matters to deal with). He is doing so well in the race to be nominated by the GOP that many people think he has won, even though the race isn't quite over. In other words, it's a foregone conclusion (at least for those people) that Romney has won the nomination.

Now let's liken this to a different situation: Assume you and I were trying to get an apple, and you had gotten it. It's your apple to lose now, because you already have it, and thus you can lose it. I can't lose the apple since I don't have it, although I could lose the contest as a whole.

So now that Romney essentially has the nomination, it is his nomination to lose; while all but one candidate will lose the nomination in the sense that they will not win it, Romney's loss (if he does so happen to lose) would be a loss in the sense of losing something already possessed.

As for popularity of the phrase, I wouldn't say it's obscure, but neither is it commonly used.

The phrase "yours to lose" means nearly the same thing as "yours to win". These phrases mean that whether you win or lose from this point onwards depends on your actions, and not on circumstances beyond your control.

"His to lose" is an indication of such a competitive advantage held by the male in question that the battle/competition may already be considered to be won by him. Any variation to the expected outcome of the competition is thus highly unlikely, but still possible.

Consider the example of the Ashes cricket match. If Australia had won the match for five years running (or whatever long period you'd like to choose) then it's "Australia's to lose" since Australia is the opposite of the underdog.

If England should win, like they did last summer, then you would NOT say it's "England's to lose" since they've not yet proved they have an overwhelming competitive advantage. Australia still has a good chance of winning. If England won the match for another two years running then the likelihood of a repeat win increases because Australia's now the underdog. Thus it would then be "England's to lose".

Although the central implication of the expression "his to lose" is that the desired goal or object is close to being firmly in the named person's possession, the expression has long had a cautionary edge as well—an implication that, although the desired thing or result may be in hand (or very nearly so), it may still be lost.

An early instance of the expression makes this double meaning quite clear. From A Companion to the Services of the Church of England for Every Sunday of the Year (1843), where the "we" refers to Christians and where the immediate objects that are "ours to lose" are "privileges":

Our privileges are ours to possess, that is our glory ; they are ours to lose, that is our care. We can keep them, we have not to gain them,—but we shall not keep them without fear and trembling ; still we have them, and there is nothing to hinder our rejoicing in them while we have them. For fear is of the future ; and that we may lose them to-morrow (which God forbid, but supposing it), is no reason why we should not rejoice in them to-day.

Of course, looming unspoken over this discussion is a more ominous implication: for devout Christians, the ultimate thing that is theirs to lose is salvation.

It may also be worth noting that a number of early instances of "[one's] to lose" are framed as negative expressions, meaning "not by rights within the power of the person to claim as his or her own." A typical example appears in Frank Leslie's Ladies' Magazine (1877) [snippet view]:

"Ah, Grace, I have lost you now for certain!" he sighed.

"I was not yours to lose," she answered, haughtily ; "I told you a week ago that I would never marry you. Now, follow me—I am going to find the judge."

The current, more upbeat idiomatic form of the expression—which tends to arise in the context of political elections or athletic contests—seems not to go back much farther than about 1980. An early instance appears in "Curse of Hornblower," an editorial published in the San Bernardino [California] Sun (September 4, 1980):

When the Republican National Convention ended, political prognosticators said things looked so good for Ronald Reagan that his path to the White House was clear and the presidency was "his to lose."

Evidently this idiomatic form was sufficiently novel that the editor thought it necessary to enclose "his to lose" in quotation marks.

Calm down to a panic..it simply means given to current circumstances he/she/we should win UNLESS someone does a monumental failure. You can dress it up all you want..but I'm a simple man..with all the usual. ???