Steve Job's untimely death taught Bill Gates this lesson

It's been six years since Steve Jobs died on Oct. 5, 2011, at the age of 56 after a years-long fight with cancer.

During his life, the iconic Apple co-founder had an intense relationship with Microsoft co-founder Bill Gates, as the pair each fought to revolutionize personal computing.

They were competitors, collaborators and, eventually, friends.

"He and I, in a sense grew up together," says Gates in a 2013 interview with CBS's 60 Minutes. "We were within a year of the same age, and kind of naively optimistic and built big companies. We achieved all of it, and most of it as rivals, but we always retained a certain respect and communication."

For Gates, Jobs' illness and death exemplified an important lesson about valuing what matters.

"[I]t reminds you that you've got to pick important stuff," Gates told ABC News in 2012, "because you only have a limited time."

The last time the pair spoke, "was two or three months before he passed away," Gates recalls in a 2014 interview with Rolling Stone. "And then I wrote a long letter to him after that, which he had by his bedside.

"Steve and I actually stayed in touch fairly well, and we had a couple of good, long conversations in the last year, about our wives, about life, about what technology achieved or had not achieved," says Gates.

Over the years, the pair had a famously complicated relationship as Microsoft created software and operating systems for not only Apple but its competitors, according to Walter Isaacson's book, "Steve Jobs."

In 1994, Jobs told Rolling Stone, "I think Bill Gates is a good guy. We're not best friends, but we talk maybe once a month."

Just three years later, Gates saved Apple when he agreed to make a $150 million investment in the company, which was then on the verge of bankruptcy.

"Apple was in very serious trouble," said Jobs in 2007 at the D5 tech conference. "Apple was very weak and so I called Bill up and we tried to patch things up." It was a lucrative move for both Apple and Microsoft.

But whatever their complexities over the years, there was certainly mutual respect.

"Steve and I first met nearly 30 years ago, and have been colleagues, competitors and friends over the course of more than half our lives," Gates writes in a blog post from the day after Jobs died. "The world rarely sees someone who has had the profound impact Steve has had, the effects of which will be felt for many generations to come. For those of us lucky enough to get to work with him, it's been an insanely great honor."

Gates sums up his opinion of Jobs concisely for Rolling Stone: "Steve was a genius."