In 1973, Xerox's Palo Alto Research Center (PARC) saw the future, and nobody listened. At least, that's the conventional wisdom, since the famed Xerox Alto personal computer never saw the light of day, even though it had e-mail, Ethernet, file servers, and a mouse-driven GUI years before anyone else. The Alto died stillborn because Xerox execs didn't think it could sell, or so the scuttlebutts say. Heck, some refused to believe it could be built, as this 1974 Xerox memo confirms, decrying the science behind the Ethernet protocol.
Except that this memo is right. If you read between the lines, the "evil exec" is noting that Ethernet wouldn't work without a control mechanism -- mechanisms that we now have in the form of routers and switches. Robert Metcalfe and David Boggs, authors of the original proposal, would go on to publish the seminal paper on Ethernet in 1976, and Xerox (along with DEC and IBM) actually helped formalize the Ethernet standard in 1980, but it was a fight all the way. Some say that fight was due to a lack of vision -- and maybe that's true -- but it's easy to kick the execs in hindsight and especially easy to forget that, along the way, a little healthy pushback makes for a better product.