“Moderate effort over a long time is important, no matter what you are trying to do. One brings failure upon oneself by working extremely hard at the beginning, attempting to do too much, and then giving it all up after a short time.”
In other words all great endeavors, such as career, are marathons not sprints. Just as a world class sprinter could never maintain their 100 meter pace for 26 miles, people can not expect to succeed instantly and consistently in a long career by treating every day and every project like a sprint because failure and burnout are the result.
If we value or causes then we owe it to them not to fail!