There is an old German hunting saying:

All skill is in vain if an angel pees down the touch-hole of your musket.

In other words: many things are outside of your control.

It is not truly a bad thing to build redundancy in a system: provided you don't over-complicate it and ADD failure points. Remember Occam's Razor. In a .40 size model the added weigh of a second battery pack may increase the wing loading to the point that it flies poorly and/or lands overly fast . . . increasing the risk of a calamity. I've got a 15-1/2 pound Giant Super Sportster that I fly with a single switch and battery. It is much easier to remember to charge one battery and keep abreast of it's condition and discharge characteristics. I check it before and during the time at the field (between flights) and have a VoltWatch 2 wired onto the model's dash so I can eyeball it just before I taxi out. But I've also got a pretty sophisticated redundancy set-up in my 27% Ultimate (THREE heavy-duty switches: two flight packs and an isolated ignition pack).

I haven't decided which is the better system. Neither has shown any signs of failure . . . yet.