There's a saying that pilots have about twin engine planes- when one fails, the other can get you to the scene of the crash. I don't fatalities are as much as 4 times as high as single engine planes, but it is certainly higher. But it's not just the opportunities for panic, and the increased skill needed to continue flying with one engine out. Twin engines are also used much more as travelling planes, so there's more pressure to make the trip in bad conditions. Recurrency training is the answer, and what a lot of insurance companies are insisting on.