An agricultural people understand that a farmer who sows expects to receive an increase back in what he has sown: each grain of wheat sown can produce an ear with hundreds of new grains, a chicken hatched from a single egg may lay hundreds of eggs over a productive lifetime, then make a delicious soup, etc.
Grains of wheat and eggs are good things. Jesus also tells us that those who sow bad things will also recieve back an increase of bad things, as in the tares that were sown in the field by the enemy in a different parable. Or in this example under discussion, where Jesus tells that those who sow the wind (a small destructive force) will reap the whirlwind (a large destructive force.)