Anicca: Impermanence
Everything that arises passes. A shadow has no length of its own; it stretches and thins as the sun moves, and a life measured in days is cast the same way, its shape decided by something that will not hold still. Qoheleth counts those days looking for a good that lasts and finds nothing among them steady enough to stand on.
Suññatā: Emptiness
Things are empty of any self or core to own. "Vain" here runs closer to vapor than to worthless: a shadow is shaped, moving, plainly there, and has nothing inside it to take hold of. A hand closes on it and comes up with air, which is what happens to a life gripped as property, and it is why the grip hurts rather than the shadow.
Avijjā: Ignorance
Avijjā is not knowing what leads into suffering and what leads out. "Who knows what is good for man in life" is that ignorance spoken aloud, and spoken by a man who has already tried wealth, wisdom, houses and gardens, and still cannot name the one thing worth doing with his mornings. The question has an answer; it will simply never be reached by adding up what a life contains.
Kammassakatā: Ownership of one's deeds
Beings are heirs to their own actions. What comes after him stays dark, though its shape is being set right now by what he does, the way an heir who takes a house takes on its debts along with its rooms. Vineyards and silver go to whoever comes next, wise or foolish; deeds go where he goes. This is the one report anyone can honestly give about what follows a man.
Appamāda: Heedfulness
Appamāda is care that does not lapse. Days as short as a shadow are the argument for it: someone who cannot know which day is his last treats each one as the day he has been given. Qoheleth arrives near the same ground by his own road when he tells the reader to eat his bread, drink his wine, and do the work in front of him while the light holds.