Gambling?
Efficiency is a key part of any professional occupation. The equipment used also needs to be efficient. Unfortunately, the best maintained equipment can mysteriously stop working, sometimes temporarily, sometimes longer and wouldn't you know it, Murphy's Law also applies to photographers.
Considering the dependency on electronics embedded into all current cameras, this issue is now bigger than it ever was!
Equipment designed for professional use costs 3 or more times the price of amateur equipment because it's specifically built for prolonged use (abuse) and able to endure rougher handling, common to time sensitive situations. The latest technology improvements are introduced in these models first, ensuring superior image quality. In fact, you get what you pay for, as it should be! In my experience, amateur equipment is simply unsuitable for serious work, even as a back up tool!
Ethical photographers invest important amounts on equipment, because we understand their true value and when it comes to critical work, such as a one time only event, back up is not something to compromise on or gamble with!
Gamblers embody poor ethics and therefore represent poor value!
I use equipment redundancy - No gambling whatsoever! 
