night having a thousand eyes, and the day one, is refering to the stars at night in comparison to the sun. If the sun goes out, everything freezes over and dies, but not much happens when stars go out. The mind having a thousand eyes is [i think] refering to how you can learn many things, adn memorize stuff, and not much happens when you forget some, but your heart having one eye is refering to true love, being with one, and when that is done, there isn't really much left that you have. Essentially saying, once you lose it and it's gone, then life becomes pointless and dark.