Dumpster diving in terms of social engineering means mingling with the insignificant to find the significant.
Step-by-step explanation:
In terms of social engineering Dumpster driving is exactly how it is in the real life.
There is no guarantee and the person diving runs a lot of risk but more that usually there is enough rewards in it if one can ignore the things that surround it.
The occasional scrounge would be able to find something very useful about the topic they are researching just like the professional divers make profits of thousands from diving into the dumpsters and finding expensive things for themselves.