When you were a child, you most likely learned a game that will serve you the rest of your life -- even if you become unaware of it. This 'game' is "as if" -- when you play cops and robbers, you are playing as if you are these things.
As you get older, some people like to pretend they outgrow such things. (I play roleplaying games, so I know better.) However, if you practice chi gung, you are visualizing and practicing "as if" there are lines of energy running up and down your body, or a ball of energy expanding and contracting between your hands and arms. No measuring device has ever successfully detected "chi," unless if you think of Kirlian photography as "scientific proof." At the same time, of course, the absence of evidence is not the evidence of absence, and most importantly, as I'm getting at -- it doesn't actually matter if there is "really" chi. Let's go on...
When you pay someone $5 for a latte, you act as if that paper represents the value that we agree upon. Any close evaluation of value-as-commodity or the value backing of money will demonstrate that the currency fundamentally represents an agreement at this level. (We're not going to get into macro-economics, where everything gets whacky.) This too is an "as if" agreement.
When you take a medication, fall in love, walk up the stairs, or do any number of other activities, you are practicing this "as if" game on some level, as, quoth Sorkin, the amount that you don't know could stun a team of oxen in its tracks. We practice it because more often than not, the benefit of playing along is higher than the cost of uncertainty.
However, many of us forget that we're playing this game at all. We start to believe in what we're playing at, that it is certain, fixed, concrete. This is where all kinds of troubles come in, from the extreme dangers of fundamentalism to mildly embarrassment of believing in something that isn't literally true.
This gets at an idea that we've repeated time and again in the posts on this site and the books that have come out of it: dream is not less real than waking (they are both states of consciousness), a metaphor is not less real than a fact (they are different claims entirely), electromagnetism is not less real than matter (they seem to exist on the same spectrum, though conversion from one state to the other requires far more than belief), ... and so on.