"Have the dogged determination to follow through to achieve your goal; regardless of circumstances or whatever other people say, think, or do." -- Paul Meyer  

"Some people plant in the spring and leave in the summer.  If you've signed up for a season, see it through.  You don't have to stay forever, but at least stay until you see it through." -– Jim Rohn  

"Develop a compulsion to closure.  Once you begin, refuse to stop before completion." -– Brian Tracy  

"There is nothing so fatal to character as half finished tasks." -- David Lloyd George

"Follow up and follow through until the task is completed, the prize won." -– Brian Tracy  

"Failure is not about insecurity.  It's about lack of execution." -– Jeffrey Gitomer