Here are some of my favourite project management proverbs and quotes (some slightly tweaked):
"One person with passion on your project is better than forty people merely interested." - E.M. Forster
"Powerful project managers don't solve problems, they get rid of them." - unknown
"A good plan, violently executed now, is better than a perfect plan next week." - General George Patton, JR
"Adding manpower to a late software project makes it later." - Brooks' Law
"Some projects finish on time in spite of project management best practices." - unknown
"There are no secrets to project success. It is the result of preparation, hard work, and learning from failure." - Colin Powell
"It is no use saying 'we are doing our best'. You have got to succeed in doing what is necessary." - Winston Churchil
Feel free to add more...