The romantization of the open call has some of it's roots in truth. Just going on one doesn't mean you're going to become a star, but it does raise your chances of doing so. Any choice made in your career with the conscious intent of influencing it's outcome in a positive way can quite arguably bring you closer to your goal. After all, if you don't go on an open call ever, you surely will not get any parts.
They tell you to wish upon a star. Sometimes a kid has nothing left except the last open call in his black organizer. The process of getting there has gotten the better of many, but it is a worthy pursuit, much better than making more nukes for a living. In fact just going on the open call itself is better than that, even if it all comes to naught. You will have been a better human being for it.
The open call represents a sort of portal into the world of stardom and fame, which if never or seldom crossed, stands much less of a chance of granting passage. Of course, miraculous things can happen at an open call, and sometimes when you go out on your first or second audition, you nail a new sitcom or get picked up for a national commercial, or get picked to star along with Eddie Murphy and Denzel Washington, and Norah Jones in a new science fiction thriller, but usually a little more time staying dedicated, staying informed, and not giving up is required.