To do so, he acknowledges, they may have to become strategically deaf.
"In today's environment, the world is full of cynics and you have to tune them out," says Cook, speaking in Scotland on Wednesday after receiving an honorary degree from The University of Glasgow.
"Because if not, they become a cancer in your mind, in your thinking and you begin thinking that you can't or that life is negative."
Watch the full speech below. (Warning, the video is not of the highest quality.)
Cook's advice is more than a pep talk. Thinking positively can actually affect the way you experience your surroundings.
"The way we expect the world to be changes the way we see it. But it also changes objective reality. It acts as a self-fulfilling prophecy," says Tali Sharot, a cognitive neuroscientist, in a popular TED talk about optimism.
"Controlled experiments have shown that optimism is not only related to success, it leads to success. Optimism leads to success in academia and sports and politics. And maybe the most surprising benefit of optimism is health. If we expect the future to be bright, stress and anxiety are reduced."
Staying positive isn't always easy, and it may require avoiding certain people.
"Even if you have friends next to you that are constantly cynics, you have to tune them out, too," says Cook. "Because if you are around it all the time, you will begin to believe and that's not good."
And despite the barrage of negative news, the present has a lot to offer, says Cook.
"The truth is, it may not seem like it all the time, but there has never been a better time to be alive than today. It is the best time ... The best time to be graduating, the best time to be in school … it's truly the best time."