Apple (AAPL) CEO Tim Cook posed a challenge for MIT graduates during their graduation on Friday when he told them to ask themselves during their careers, “How will you serve humanity?”

Cook focused his highly anticipated speech on his own experience trying to find meaning in his career, which he ultimately came upon when he joined Apple 20 years ago.

“There will be days where you will ask yourself where’s all this going? What is the purpose?” Cook told the graduates. “What is my purpose? I’ll be honest. I asked myself that same question and it took nearly 15 years to answer it.”

When Cook first joined Apple, the now-deceased co-founder Steve Jobs had just returned to the company and was reinvigorating it with the mission to “empower the crazy ones.” But there was a larger mission at Apple that ultimately became Cook’s, as well.

“I was never going to find my purpose working someplace without a clear sense of purpose of its own. Steve and Apple freed me to throw my whole self into my work … To embrace their vision and make it my own. How can I serve humanity?”

‘Don’t listen to the trolls and for God’s sake don’t become one’

During his speech, Cook acknowledged to the graduates that technology, with all of its potential for good, can also be ugly and divisive.

The internet, he said, “can also be a place where basic rules of decency are suspended and pettiness and negativity can thrive. Don’t let that noise knock you off course.” Cook added: “Don’t listen to trolls and for God’s sake don’t become one.”

In an apparent reference to President Donald Trump’s trolling online, Cook made a joke at the start of his speech when he accused MIT’s students of taking over the president’s Twitter account as part of their proud tradition of pulling pranks.

“I can tell college students are behind it because most of the tweets happen at 3 a.m,” Cook joked.

Joking aside, Cook urged students to always consider the human beings their technology would ultimately serve. He named examples of people whose lives were touched by technology, such as a blind person who could run a marathon with the help of an iPhone or a child with autism who could connect to the world with their iPad.

“When you keep people at the center of what you do it can have an enormous impact,” he said.

Cook’s humble roots

Before he was CEO of Apple, Cook served as the company’s chief operating officer. Prior to that he was at Compaq and at IBM (IBM). Cook has humble roots, having grown up in Robertsdale, Alabama, current population 5,276. His father worked in a shipyard in Mobile, Alabama, and his mother sometimes worked at a local pharmacy, according to the Washington Post.

Cook earned his bachelor’s degree in industrial engineering from Auburn University in 1982 and later got an MBA from Duke University’s business school.

Two years ago, Cook gave the commencement speech at George Washington University, telling graduates not to shy away from taking risks.

“The sidelines are not where you want to live your life. The world needs you in the arena. There are problems that need to be solved,” Cook told those graduates. “Injustices that need to be ended. People that are still being persecuted, diseases still in need of cure. No matter what you do next, the world needs your energy.”

Erin Fuchs is deputy managing editor at Yahoo Finance.

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