As other pages on this site show, I am fascinated by the designed objects people make when they are operating under heavy constraints. Consider, as an example, the prisoner in a maximum-security penitentiary who has to make a shiv if he wants to survive. He is not allowed access to the tools or materials a profesional knife-maker might employ, or even the kinds of things a caveman might find on a walk through the jungle primeval. He has to use what's at hand. He has to be clever. He has to be sneaky. The finished thing has to work well enough to protect his life. For a fascinating (if somewhat depressing) look at the kind of inventiveness such harsh conditions can inspire, I recommend Improvised Weapons in American Prisons, by Jack Luger.
The lesson designers can take from prisoners is that constraints are the way to inspire really creative and clever solutions. Consider the problem represented by the tools on this page: Given a material (steel) and a process (machine-stamping), what is the most useful profile we can design? Because the manufacturing process dictates a fundamentally 2-dimensional design, the profile is the entire problem. So browse over the solutions on this page, and then pose the problem to yourself: What is the most useful shape for a piece of flat steel? How many functions can you combine? How easy is the resultant tool to use?