Apple CEO Tim Cook has revealed that after hearing about the death of Apple’s late CEO and co-founder Steve Jobs someone had to “kind of shook me” and tell him: “it's time to get on”. And as a result he replaced the sadness he felt with an “intense determination”.

On hearing of Jobs’ death last October, Cook revealed that: “It was absolutely the saddest days of my life when he passed away”.

The news, while expected, was still a great shock to Cook and he revealed that he dwelled on it until he replaced the sadness with “intense determination”.

He said: “Maybe as much as you should see or predict that, I really didn’t. But at some point, late last year, somebody kind of shook me and said, it’s time to get on. So that sadness was replaced with intense determination to continue the journey. So that’s where it is today.”

Cook described Jobs as a “genius and a visionary” during his chat with Kara Swisher and Walt Mossberg at D10. He also noted that while Jobs was “the best person at the world at doing this”, but Jobs would “flip on something so fast that you would forget that he was the person taking the 180 polar position the day before.”

Discussing Jobs tendency to change his mind and claim an idea he had dismissed previously as his own (as discussed in the Walter Isaacson biography), Cook revealed: “It was an art. He would never know that he thought the opposite. I saw it daily! And this is a gift, because things do change. And it takes courage to change, and courage to say, I’m now wrong. Maybe I was right before, maybe not, maybe I was never right.”

Cook also described Jobs as “irreplaceable” but he claimed he has never felt the need to try to “be Steve”.

“Steve was an original. I don’t think there’s another one of those being made,” Cook said. “I’ve never viewed my role as to replace him,” he said, adding: I’ve never really felt the weight of trying to be Steve. It’s just not who I am. It’s not my goal in life. I am who I am, and I’m focused on that and being a great CEO of Apple.”

Cook might be his own person, but he revealed that he “learned a lot from Steve,” in fact he learned enough that “we could be here all night, probably all week, maybe even a month,” he joked to Swisher and Mossberg.

What did Cook learn? “I learned focus is key, not just in running a company but in your personal life as well. That you should do only a certain number of things great, and you should cast aside the rest.”

Jobs also taught Cook that focusing on excellence is important. “In business, honing the key technology of the product. Steve was always focused on that. Always expecting the very best. Apple has a culture of excellence that I think is so unique,” he said.

And most pertinent of all: “He also taught me that the joy is in the journey, which was a revelation for me. And he taught all of us that life is fragile, and that we’re not guaranteed tomorrow, so give it everything you’ve got.”

Another tip: don’t dwell on mistakes. “Another thing Steve taught us all was not to focus on the past. Be future focused. If you’ve done something great or terrible in the past, forget it and go on and create the next thing.”

Cook also revealed details of the conversation he had with Jobs when Jobs asked him to take over as CEO. During the conversation Jobs revealed his concerns that people would ask “what would Steve have done”.

“Steve told me, when he called me to his home to talk about being the CEO and subsequently the discussions we had, he told me, ‘you know, I witnessed what happened at Disney when Walt passed away.’ He said that people would go to meetings… and all sit around and talk about, ‘what would Walt have done? How would he view this?’

“And he looked at me with those intense eyes that only he had, and he told me to never do that, to never ask what he would do. Just do what’s right. And so I’m doing that,” Cook explained.

Going back to his first meeting with Jobs, when Jobs recruited him, Cook said that he wanted to join Apple just five minutes into the conversation. “It was a very interesting meeting… and the honest to god truth, five minutes into the conversation I wanted to join Apple. I was shocked at this. It wasn’t how I went into the conversation.”

Cook revealed that he nearly didn’t go for the job: “Steve had hired an executive-search firm to find somebody to run operations and I’d turned down meeting and they kept calling and I eventually said I’d talk. I had no time, so I flew out Friday on a red eye for a Saturday morning meeting with Steve.

How did Jobs win Cook over? “He painted a story, a strategy, that he was talking Apple deep into consumer at a time when I knew that other people were doing the exact opposite. And I never thought following the herd was a good strategy. You’re destined to be average at best. So I saw brilliance in that.”

“And he told me about what would later be the iMac, and I saw brilliance in that. And I saw someone who was unaffected by money. That’s always impressed me. So those three things, I thought, I’m going to throw caution to the wind and do this. I went back and resigned immediately,” Cook said.