You are at a pub (or a beer bar, or whatever, you know what I mean). You're not alone, you're with a bunch of people. You aren't there for a tasting or any other beer-focused thing, you're there simply to hang out with those people, and that place was chosen because everybody liked it enough, or whatever.
You order a beer, it's not the first of the day, maybe not even the first of that session; and it's a beer you've drunk already several times, though you don't drink it too often. There's nothing in that beer that makes you look forward to it any more than you look forward to any other good beer you know. You ordered it for the sole reason that at that where and when you fancied drinking something like that.
You get the beer, you thank the person that brought it to you with a nod, and you carry on with the conversation your were having, or listening to the story one of your friends was telling, whatever. The glass of beer you've just got is just another thing in the whole.
When the time has come—maybe you finished saying what you had to say, or or chewing what you were chewing, or you don't want the head to fall—you take the first sip, or rather a proper swig of that beer.
And that's when it happens. Maybe it's only a split of a second, maybe longer. But it happens. When that swig fills your mouth, the whole world comes to a stop, and your senses become part of a vortex. You feel like you are starring in a cliché of a TV advert, and you don't mind it one bit.
You exhale, put the glass down, looking at the beer, and seamlessly go back to reality, knowing you've just found the answer to the question of what makes a beer great.