Some plants are prolific; some are not.
Dandelion seeds float through the air and disperses far and wide in spring or summer; hundreds of tiny seeds burst from the spent blooms of cleome as a sphinx moth feeds at dusk; and you can just walk past some hairy cress and millions of seed burst forth from the draft.
Woody plants seem to be a bit more elusive. I have never seen a Serbian spruce spring forth from a fallen cone or an apple tree emerge from rotten fruit beneath the canopy.
Starting woody plants from seed can be a bit more tricky.