Long, long ago in a galaxy far away, something went boom. The result was an outburst of sub-atomic stuff, some of which eventually found its way here.
That kind of scenario was repeated pretty often and still more of those sub-atomic things are headed this way. As they arrive, they will get here quite dispersed, so much so that single ones of them will be individually detectable. Unfortunately, when the thing that does that detection is a semiconductor that you cleverly designed into your product, the result is called a single event upset and in some cases, it can be quite damaging. This is especially of concern if your product is in earth orbit or is zipping along elsewhere out in space.
Consider for example a push-pull inverter made with MOSFETs. If the "off" side MOSFET gets spuriously turned on when it shouldn't be turned on, the result can be a near short circuit to ground of the driving rail voltage. An event like that could be catastrophic.
This sketch shows such an inverter but with protection against a catastrophe arising from such a single event upset.
Figure 1: Each "X" marks a MOSFET undergoing a single event upset.
Whichever MOSFET gets turned on by a single event upset, the three remaining switch positions will preserve the switching scenario until the struck one can recover.
In this circuit, a single event upset will momentarily upset the transformer drive balance a little, but it won't allow a potentially catastrophic pull down on the +Vcc rail because the companion MOSFET of the affected one sustains the intended switching.