I'm not a huge fan of either Thoreau or of Transcendentalism, but I do find Thoreau to be quotable--even when I don't agree with him. One of my favorites from Walden is this:
"If you have built castles in the air, your work need not be lost; that is where they should be. Now put the foundations under them."
One line so often recalled as one observes people is "The mass of men live lives of quiest desperation."
However, on a more positive note here are others from Henry David Thoreau's work, Walden:
If you have built castles in the air, your work need not be lost; that is where they should be. Now, put the foundations under them.
I learned this, at least, by my experiment; that if one advances confidently in the direction of his dreams, and endeavors to live the life which he has imagined, he will meet with a success unexpected in common hours.
I have a great deal of company in my house; especially in the morning, when no one calls.