Facilitating change is more effective than attempting to prevent it. Learn to trust in your ability to respond to unpredictable events. It’s more important than trusting in your ability to plan for disaster. Martin Fowler and Jim Highsmith
I have always found that plans are useless, but planning is indispensable. Dwight Eisenhower.
Debugging is twice as hard as writing the code in the first place. Therefore, if you write the code as cleverly as possible, you are, by definition, not smart enough to debug it. B.W. Kernighan.

It's hard enough to find an error in your code when you're looking for it; it's even harder when you've assumed your code is error-free. - Steve McConnell.
Better train people and risk they leave - than do nothing and risk they stay.
Why do we never have time to do it right, but always have time to do it over? - Anonymous