Pumpkin seeds

You can do two things with pumpkin seeds. Eat them, an excellent source of protein, or plant them, and watch a successful seed bring back 100 more.

The farmer who plants the seeds aggressively, without regard for, "hey, be careful, I could have eaten that seed," often ends up with many more pumpkins and many more seeds. On the other hand, the person who guards all the seeds and then eats them ends up with not much.

And of course, money works the same way. Time, too.