People often overestimate what will happen in the next two years and underestimate what will happen in ten.

Bill Gates (b. 1955) American software magnate [William Henry Gates III]

The Road Ahead, “Afterword” (1996 ed.)
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First use of this specific formulation, but similar phrases can be traced back to the 1960s. More discussion of variations on this theme: People Tend To Overestimate What Can Be Done In One Year And To Underestimate What Can Be Done In Five Or Ten Years – Quote Investigator®.