It's very hard for you or I now, to appreciate what it was like before you learned to think of linked lists as stacks. The point is, there is definitely a leap of insight necessary if you've never thought of things in this way before. I was 12 or so when I made the leap, and I guess I'm slightly lucky that I remember the exact moment for this particular case.
I don't think I knew what a linked list was at age 12, but I don't think you even have to know what a stack is to do this. Just draw it on a whiteboard, and it becomes obvious that you just walk the list and flip arrows. Seeing that linked lists can represent interesting structures is I think an even more advanced concept, but one that is unnecessary for this particular question.
