I'm stupid.

You're not the only one. Clearly, I need to read more.

Sorry, been a bit busy at work and hav'nt had time for anything else. That said, let's try something a bit easier for the next quote.
'A person who is said to be proficient at the arts is like a fool. Because of his foolishness in concerning himself with just one thing, he thinks of nothing else and thus becomes proficient. He is a worthless person.'
Well, good luck!!

Good choice.

I'll stay out of this one.

Sounds like something from 'Hagakure'?

You got it!!
I just KNEW there had to be more than two people here who could answer that one...now if only we can get everyone else to give it a shot. Well, congrats. You get to choose the next quote Harlan.

"The occurance of a single thought, or an attachment to something are both sicknesses. The mind of No-Mind arises when you expel attachment. This is the absolute ultimate."

Sorry Harlan,
Thought I'd give someone else time to think of an answer. (Actually, was a bit stumped, though I know I have heard this one several times before in the past).
Without checking any of my books, I'll just quess and say it might be from Go Rin no Sho (The book of five rings) by Miyamoto Musashi. That's probably wrong, though. If he had said it, he would have most likely gotten it from an older source. Any hints coming our way?
As far as the meaning behind the quote, I think that I'll use another quote from Takuan Soho to explain it:
It is the very mind itself that leads the mind astray; of the mind, do not be mindless...

Sorry...too obscure a quote.

Tsuki no sho, by Yagyu Jubei Mitsuyoshi

Some info on the fellow:

http://www.furyu.com/archives/issue9/jubei.html

How about this one:

"The Way of the martial arts is in deception."