Overconfidence or over optimistic?

I'm still having some trouble wrapping my head around these two concepts - how different are they? For instance, do people accept risky assignments because they are confident or optimistic?
All of the pilots knew that the Cessna Caravans, aircraft designed to carry about 10 passengers but modified for surveillance work, were ill-suited for the task at hand. El Dorado airport itself is more than 8,300 feet above sea level, where the air is so thin that the Caravan pilots could not take off with the extra weight of full fuel tanks. They typically left Bogotá with only enough gas to fly down to the Colombian military base at Larandia, where they topped up before setting off on missions that kept them airborne for four to five hours.

With precious few spots for emergency landings in the Andes, the pilots felt vulnerable flying with only one engine. “In a two-engine aircraft, you lose one and you shut it down, start troubleshooting, and have time to consider your options,” said Hooper.

But as veterans with long records of service, the pilots felt capable of safely flying the aircraft beyond what others considered its limits. “It’s called pushing your luck,” Hooper said. “We were stupid but lucky, and we knew it, but experience counts for a lot in these situations. We were comfortable doing it, at first.” ...

More and more often, the small unit was asked to fly higher and higher, and deeper and deeper into dangerous country. In the summer of 2002, after flying for more than a year, Cockes, then the unit’s lead pilot, stood up at a company all-hands meeting in Bogotá and expressed concern about this “mission creep,” warning that the single-engine Cessnas were no longer safe. He and the other pilots were willing to keep flying, he said, but wanted a commitment from the company that they would transition to twin-engine planes, which the aircraft supplier was willing to offer at no extra cost.

The company said no and the rest is history:

Those pilots, Paul Hooper and Doug Cockes, predicted that the single-engine Caravan would be unsafe for high-tempo missions over the Andes Mountains. After program managers on site in Bogotá dismissed their warnings, the pilots wrote letters in the fall of 2002 detailing their concerns to company officials, including Kent Kresa, then the chairman and CEO of Northrop Grumman. For their pains they were demoted, reprimanded, threatened with lawsuits, and, in their words, “pushed out” of the program shortly before their predictions came tragically true. They consider themselves fortunate. “The only reason those three Americans were captive on the ground for five years, and the reason why five of their colleagues are now dead, is the greed and incompetence of California Microwave and Northrop Grumman,” Hooper told me.

From Flight Risk by Mark Bowden.