Often with the things we want in life- even when we get them, it's only moments before we want something else. We're always hoping that each desire, once met- will be the one that finally completes us, finally gives us lasting contentment. We say to ourselves: "okay, I thought it would be that last thing- but really it was this thing- THIS will be the thing that will make me happy forever!" Wash, rinse, repeat. Over and over. I think there is purpose in ambition, in setting goals- but a misplaced expectation can cripple your gratitude and shorten the lifespan of your happiness once you've attained something. The trick I think, is to let your goals evolve over time rather than become a never ending list, or in the case of this poster's metaphor, a never ending line of people- each dressed in their most attractive attire and hoping that they convince the bouncer that they deserve to get in- but once inside are just another anonymous face in a dimly lit room with loud music that is difficult to hear anyone speaking over.