Complacency is similar to the pause taken by a lazy colt when it chooses to go back to the stable than opt to run the race further to the goal post.
Given the choice between putting in efforts to win and inaction that makes one pull out of the race, relax and enjoy, the complacent man opts for the later. One wins accolades and rewards. The other thrives on moments of purposeless relaxation on the way to its graveyard.
A man who knows his job, sees much more that needs to be done than what has already been done such that he is always pressing forwards and never gives up an instant of thought to how good and how effective and effecient, he is.
Thinking always ahead, thinking always of trying to do more, bring a state of mind in which nothing is impossible. Says Henry Ford ... the moment one gets into the 'expert' state of mind, a great number of things become impossible.
If you believe you are the tops, you will stop further climbing.