It's like LEGO's. The blocks are sturdy and the rules of how blocks fit together are simple. But building a mini Taj Mahal is still not easy. You do have to know basic physics & structural engineering, but if you do, the task is very do-able. Even fun.

Unlike if you were building a mini Taj Mahal out of match sticks, Elmer's glue, rope, and playing cards. Even a professional structural engineer would have a hard time with that. The rules of gluing a match stick and a playing card together are already complex (not to mention uncertainty about where to rope fits in), and it that makes it that much harder to make a final product.

This video goes into "simple" vs. "easy" https://www.infoq.com/presentations/Simple-Made-Easy