The Riddle of Time

A wise man was on his deathbed. He called his three sons into his room and posed a riddle to them. The eldest brother, trim as possible and taller than certain trees spoke first. What is as round as a circle and as straight as a line? It costs you no money. And yet if you lose it, all is lost. You can heat it up, but this is only what fools would do. Why does two men speak next? Loudly and confidently. Of course our dear father is describing time. So it fits these descriptions.