The only way to think outside the box is to know where its edges are. You can think inside the box without being aware of the box: you can only make a choice to stay inside the box when you know what comprises the box, the materials of which it is made and its limits.
Imagine a box. The box has a top painted like the sky, and a bottom that rests on the ground. The sides are painted to show a reasonable facsimile of the horizon in all directions. You can live inside the box indefinitely as long as you do not explore its limits. All the choices you make will be based on assumptions about the world that are based on what it is like inside the box.
Everything is fine until you come to the end of your world. In most stories, there is water at the end of the world, a way of saying metaphorically that the edges are more fluid than they look and it is possible to flow over them and into something bigger than the box we thought was the whole of the world. Sometimes things flow into the box from the other side, and the walls of the box have to grow. Telecommunications, for instance, came from somewhere outside the box and changed how we live inside it. The impossible became improbable, and then possible, and then habitual.
Some of us live in narratives that act like boxes. We are the heros of adventure stories, or hard luck stories, or success stories. We hit the limits of the story when someone wanders into our life from a different kind of story entirely: they are happy in the midst of a tragedy; they are magicians in a scientific experiment or scientists in a world governed by ritual or money. We have to decide whether to kick such people out of our stories or to rewrite our stories to include new elements.
Think of a particular problem. Allow yourself to become aware of everything you know about the problem, and then of all the beliefs and presuppositions that sit just outside what you know, supporting what you know by giving it walls and limits. The limits keep the problem within bounds: otherwise, the whole universe might go off-kilter and there would be nowhere to go for new resources to solve the problem. The resources must come from outside the walls, and you cannot find them until you run into one of those walls and notice where it is and what it is made of. Only then can you go under it or over it or through it, to get what you need. And then you will repair the wall.
There is nothing wrong with the box. Or with being inside the box. Or with being outside the box.
It is good to explore the box. So you can move walls instead of running into them.