Strange as it may seem, I still hope for the best, even though the best, like an interesting piece of mail, so rarely arrives, and even when it does it can be lost so easily.

This quote is expressing that even though something positive and good may be a rare occurrence and quickly lost, the person still has hope that good things can happen in their life. It is comparing rare positive occurrences to like pieces of mail. Mail can be sent, but it can also get lost, so although something can arrive, it can also be lost easily. Despite this, the person stills maintains hope for the best.