Life is like riding a bicycle. To keep your balance you must keep moving.

· Albert Einstein

Life can only be understood backwards, but it must be lived forwards.

· Soren Kierkegaard

No man ever steps in the same river twice.

· Heraclitus

Progress is impossible without change, and those who cannot change their minds cannot change anything.

· George Bernard Shaw

If there is no struggle, there is no progress.

· Frederick Douglass