Plane Geometry begins with five axioms (assumptions) and builds an entire branch of mathematics from that. The axioms are the framework of the box, and the resultant proofs are only accepted when methods are shown to be inside the box. If you change even one assumption, you build a different kind of geometry and define a different box.
One of the great intellectual accomplishments of all time was Sir Isaac Newton's three laws of motion and the calculus invented to provide a mathematical basis for them. If ever out of the box thinking took place, wouldn't this be such an occasion? The idea was certainly original, but Newton framed his ideas with tools he created in a box of his own invention. Modern science starts by building the box first as a frame of reference.
Finally, consider Jefferson's concept of inalienable rights. He called them self evident truths, making them his axioms and defining the shape of his box. Others might question whether they were true, or if they were self evident, or what rights are inalienable, but in all cases the box structures the thinking whether you accept the assumptions or not.
Even when ideas make radical changes, the process is the same. Commerce and development were the result of one set of assumptions, ecology and green living the result of another. Even cradle to cradle thinking about a sustainable future is redefining the box.
That's the riddle: rational thinking is the process of connecting inspired ideas to some framework and exploring the resultant consequences. Imagine coming into a darkened building. Just as you turn on a light as you enter to see inside a room, inspiration lights up the box so we can see what is inside it.
We always think inside some box. This is great news. By adding to our tools and redefining the shape of our box, we add new rooms to our intellectual building which we can fill with resultant discoveries. If you gave a problem you can't solve, look for another tool or another box. Don't try to think outside the box. Look for a better box.