Sir Robert Walpole's comment on initial enthusiasm for ill-considered actions.
"Now they ring their bells; in a few weeks they'll be wringing their hands."
Quite an appropriate comment on our involvement in Afghanistan; as is another Walpole quote "It was easier to conquer it than to know what to do with it.".
Some other quotes from Walpole
The world is a tragedy to those who feel, but a comedy to those who think.
The whole secret of life is to be interested in one thing profoundly and in a thousand things well.
History is a romance that is believed; romance, a history that is not believed.
Nine-tenths of the people were created so you would want to be with the other tenth.
Serendipitous discoveries are made by chance, found without looking for them but possible only through a sharp vision and sagacity, ready to see the unexpected and never indulgent with the apparently unexplainable. [e.g. the discovery of penicillin]