If you're not stubborn, you'll give up on experiments too soon. And if you're not flexible, you'll pound your head against the wall and you won't see a different solution to a problem you're trying to solve.
To live is to be constantly learning.
真正的美国发现还在我们面前。我们精神、我们人民、我们强大而不朽的土地的真正实现,尚未到来。