Signing for Real Madrid should be the height of any footballer's ambition, they're the biggest club in the world and constantly attract the biggest stars, to sign for Real Madrid is to become a star, to achieve your life goals. Despite all their failings, not much can go wrong once you sign for Real Madrid. If you succeed, you go down in history as one of the best ever, if you fail, you're pretty much guaranteed a move to another big club anyway, rarely does a player leave Real Madrid for a terrible side, and for Kolarov it'd be a step up from Lazio, so he has nothing to lose.
But, aside from all of this, to make it as a professional footballer you generally have to have a lot of confidence in your own ability; should you have this you should be of the mindset that you will go to Real Madrid and succeed.