This article is by no means a reference in streams concept.
It's a simple discussion between friends :-)
If I had to explain the streams to a non developper, I would simply say that, at the basic, streams concept is the port of Excel SpreadSheet concept to programming language.
In a spreadsheet when you enter in a cell [C1] : [C1] = [A1] + [B1], your clearly establish a relation between those three cells.
In doing so, you are clearly stating : "the content of the cell [C1] is the result of the sum of the content of the cells [A] and [B]
And because you established a relation and not a simple affectation, you expect that, whenever A1 or B1 are modified C1 is modified automatically, whithout any action from you.
Thank you for reading.