If only "trying things" always equaled "developing things". There's a whole body of knowledge (under the Lean Startup umbrella) that argues otherwise.

Do we always have to build it before we know that it will work (or, in 9 cases out of 10, that it will not work)?

Even more so, do we have to build a fully-fledged version of it to know?

If yes, then I agree, development is the bottleneck.