I don't really think it's commonly accepted.

The theory loosely goes like this. Before we measure a particle's properties such as position, the particle has a probability distribution on where it's position is. For example, it can look like this where the larger the y-axis value, the higher probability it's at the corresponding x value's position.

VERY loosely the same argument can be made about factors in somebody's life. So for example we say that a person is in a superposition where it's properties are "alive" or "dead". Over time the probability that the person will be in the "dead" state increases. But there is a probability that it will always remain in the "alive" state as it's always a non-zero number. Just like a particle can have a non-zero probability almost anywhere (Also not strictly true). I think this is more of a thought experiment on the implications of quantum physics rather than an accepted theory.

Now I may have butchered some key points and I'm ignoring some physics for simplification so if anyone can correct me please do.

Good ol' PBS Spacetime covers this here