How often have technological solutions proposed by “experts” been incomplete, misleading, unrealistic, or just plain false?

In the 1957 issue of Popular Mechanics Magazine, a car called a “fan” would allow one to avoid the need to construct costly highway systems across the nation.

When would these cars be on the market? “A rough guess is that in about 10 years [1967] you’ll be able to buy a four-place fan for the price of a good car. How can engineers be so sure about something that hasn’t been flown yet, or even built? For one thing, [the design is rudimentary . . ]”

It's now 2005 and, as the kids might ask, "Are we there yet?!"