Good Design

What makes good design?

I came across an ancient instance of good design in Plutarch's Lives, on his chapter on the Spartan lawgiver Lycurgus. Plutarch describes a cup the Spartans used in war:

"the Laconian " kothon ," or drinking-cup, was in very high repute for usefulness among soldiers in active service...",

"For its colour concealed the disagreeable appearance of the water which they were often compelled to drink, and its curving lips caught the muddy sediment and held it inside, so that only the purer part reached the mouth of the drinker."

Can design get any better than this?