The definition of "windfall" as a unforseen
gain actually came about as a combination of
definitions. The
gain mentioned actually *did* come from the
fallen fruit extension. For a goodly time, it was of course
stealing to take
apples or other fruit from
orchards belonging to anyone else, and this
crime would be prosecuted. However, under an unspoken
rule, any fruit that *fell* from the tree naturally, and was on the ground, was
free for the taking. So whenever
wind (unpredictably) knocked down
crops, anyone could take the
profit for themselves.