The single biggest threat to sustained success

"If you have a business that competes with one of mine, I am going to try to kick your ass and put you out of business. I presume that you are trying to do the same thing [to me]…which is why I always try to look at each of my businesses from the perspective of my competition. I think, 'If I wanted to put my company out of business, what would I do? If I wanted to take customers away, what would I, as a competitor, do?' " - Mark Cuban, businessman, investor, and owner of the Dallas Mavericks
"Business success contains the seeds of its own destruction. Success breeds complacency. Complacency breeds failure. Only the paranoid survive." - Andy Grove, businessman, engineer, and author
“Complacency kills, and what causes complacency? Success." - Robert O'Neil, former Navy SEAL (Senior Chief Special Warfare Operator)

When three people with track records as strong as those above independently speak out and agree on something, it's worth listening to.

All leaders are focused on success, whether it's defined as company growth or a completed mission on the battlefield. What happens next, though, determines the sustainability of success. Great leaders aggressively pursue ongoing improvement. Other leaders rest on their laurels after a "win." The former understand that innovation is more than a goal. It is survival. The latter learn it the hard way. 

The single biggest threat to success, then, is success. Or, more accurately, how leaders respond to it.