Prototyping is the lingua franca of innovation.  It externalizes internal thinking in a tangible form, rendering it more intelligible by others and the world.  The good news is that, though it has its roots in the creation of physical things, when taken as a mindset and a methodology, as a way of finding solutions, prototyping can be applied to any domain.  Anything can be prototyped, and you can prototype with anything.

Anything can be prototyped. Prototypes aren’t just for physical products. I routinely see people
prototyping services, complex experiences, business models, and even
ventures.  Really, anything can be prototyped: before filming Le Mans,
Steve McQueen took a film crew to the French race a
year earlier, shot an entire movie's worth of stuff, and then threw most of the exposed
stock away.  He knew that they best way to learn how to
shoot a great movie at Le Mans was to first shoot a rough movie there.
His camera people gleaned deep insights into camera placements, mounts,
and techniques which put them in good stead when it came time to shoot
the real movie. And the value of the tacit knowledge transfer involved
cannot be underestimated: rather than try to explain to new camera
people what he wanted, McQueen could point to actual film clips and
say, “This is good.”  Prototyping leads to speed as a process outcome.

You can prototype with anything.  You want to get an answer to your big question using the bare minimum of energy and expense possibly, but not at the expense of the fidelity of the results.  It's not only about aluminum, foamcore, glue, and plywood.  A video of the human experience of your proposed design is a prototype.  Used correctly, an Excel spreadsheet is a wonderful prototyping tool.  GMail started out as an in-market prototype.  A temporary pop-up shop is a prototype.  Believing that you can prototype with anything is a critical constraint in the design process, because it enables wise action, as opposed to the shots in the dark that arise from skipping to the end solution because zero imagination was applied to figuring out how to run a create a prototype to generate feedback from the world.

A wise person operates with the worldview that anything can be prototyped, and we can prototype with anything. 

This is the fifth of 21 principles.  Please give me your feedback and ideas.