"There are three kinds of people. One kind is the dumb ones who don't learn. The smart ones who learn from their own mistakes. Very smart ones. But then there are the wise ones, the ones who learn from other people's mistakes."
-- not sure

Several

Ran across some great quotes (and individuals) on Jonathan Stark's web site. Below are some of my favorites:

In times of change, the learners will inherit the world and the learned will find themselves beautifully equipped to deal with a world that no longer exists. - Eric Hoffer

Act as if what you do makes a difference. It does. - William James

There are no secrets to success. It is the result of preparation, hard work, learning from failure - Colin Powell [I continually encounter folks who put in the hard work, but lacking in either preparation or, more importantly, learning from failure... and I'm not innocent either. -jr]

Why do you wake up in the morning and do things? If you can't answer that, you might as well end it now. - Peter Baer

The measure of success is not whether you have a tough problem to deal with, but whether it's the same problem you had last year - John Foster Dulles

A problem well stated is a problem half solved. - Charles F. Kettering

A witty saying proves nothing. - Voltaire

Security is mostly superstition. It doesn't exist in nature. Life is a great adventure or it is nothing. - Helen Keller

I do not know with what weapons World War III will be fought, but World War IV will be fought with sticks and stones. - Albert Einstein

Every man takes the limits of his own field of vision for the limits of the world. - Arthur Schopenhauer

Sometimes you get the best light from a burning bridge. - Don Henley

There is no security on this earth, there is only opportunity. - General Douglas MacArthur

Learn from the mistakes of others. You can’t live long enough to make them all yourself. - Eleanor Roosevelt

Try not to become a man of success but rather to become a man of value. - Albert Einstein

Happiness depends upon ourselves. - Aristotle

In preparing for battle I have always found that plans are useless, but planning is indispensable. - Dwight D. Eisenhower

Always do right. This will gratify some people and astonish the rest. - Mark Twain

It is the mark of an educated mind to be able to entertain a thought without accepting it. - Aristotle

Do what you feel in your heart to be right - for you’ll be criticized anyway. You’ll be damned if you do, and damned if you don’t. - Eleanor Roosevelt