I tend to agree with IO540 in supposing that theoretically you have double the chance of engine failure with a twin.
That's really not the case. The truth is you have the same chance with everything, every time. Either it will, or it won't. Period. This doesn't increase with engines, with numbers of takeoffs, with anything. Either it will, or it won't. Either it will run, or it will fail.
One would imagine with four engines we'd be having failures right, left and center with odds and chances increasing in proporition to the number of engines...but suprisingly, no.
In a light piston twin, the second engine isn't there for safety. It's there for performance. Specifically, climb performance. Many light piston twins won't maintain altitude on one engine, let alone positive climb performance, and have very low single engine service ceilings. While this is often cited as a big disadvantage for the light twin...it's a given that singles don't have many options during a power loss, either.
One of the big advantages of a twin is redundancy of systems; additional hydraulic pump, additional vacum pump, additional generator, etc. Learning to fly a multi engine airplane, or any advanced or complex airplane for that matter, is learning to fly it with engines and systems failed...learning to handle it in less than ideal conditions.