One thing I tell new quants that I hire is that your job is kind of like a magic trick. To an outside observer the trick looks almost supernatural, but once you understand the trick you realize it's so unbelievably simple and straight forward you wonder how it is you were ever fooled by it.
That said, even if someone tells you how a magic trick is performed and then hands you everything you need to perform it, you are almost certainly going to mess it up. It takes a lot of practice, skill and discipline to pull off even a simple magic trick even after you fully understand it. All of the difficulty of a magic trick is in the execution, not in the idea.
It's the same with quantitative finance, the techniques do not involve anything remotely complex like quantum mechanics and in fact I am almost certain to reject strategies that are overly complex... but even if I revealed how our simplest of trading algorithms work, it's still incredibly difficult to actually execute them. Taking an idea and translating it into a high performance algorithm that is bug free, dealing with networking, collecting and dealing with petabytes of data, having a tight iteration loop, risk management, and most of all, having the creativity to identify something simple among a sea of complexity, those are what make my firm and other firms successful.
It's unbelievably difficult work and most quants do end up failing, but it's not difficult in the way that many people think it is. If anything, most quants I've worked with fail by overcomplicating things and not being able to work from the ground up, off of first principles.