Here’s a way I heard Omar (I think) describe it…
Think of the object like a suitcase and the data block is everything inside the suitcase. If you create a normal duplicate, the suitcase and everything inside it get duplicated. Initially, it will look like the same suitcase. But if you go “inside the suitcase” (go into edit mode) and change something, the new suitcase will no longer look like the original one. But if you create a linked duplicate, all the data inside is still the same, so even if you go inside (edit mode) and change something, all the other duplicates that are linked and still have the same “data block” inside the suitcase. In Object mode (when you’re not inside the suitcase), you can move each suitcase to a different place, scale it, and/or rotate it, but the contents inside the linked duplicate will remain the same (just in proportion to whatever changes you made in object mode).
