Toy problem to motivate the idea of advanced Green's functions

[Swamp Thing]

The Wikipedia article on Green's functions says,

the solution provided by the use of the advanced Green's function depends only on the future sources and is acausal. In these problems, it is often the case that the causal solution is the physically important one. The use of advanced and retarded Green's function is especially common for the analysis of solutions of the inhomogeneous electromagnetic wave equation.

What would be a really simple physical toy problem that would motivate and explain the concept of advanced Green's functions?