Over a series of 14 tweets posted Monday, the world’s richest man used the words “impact,” “happiness,” and “progress.” He did not mention money. Instead, he told the graduates what jobs he would be looking for if he started out today.

“AI, energy and biosciences are promising fields where you can make a huge impact,” he wrote. Earlier this year, Gates—who famously dropped out of Harvard to found Microsoft—said that artificial intelligence had “phenomenal” potential, and “anything connected with that would be an exciting lifetime career.” In the same speech at Columbia University, he said there is a huge growing demand in the energy sector to develop “reliable, cheap, and clean” energy. Similarly, developments in biotech were moving “faster than ever,” he said, with a need for innovation to combat diseases such as cancer and obesity, and developing vaccines.

As well as urging new graduates to surround themselves with “people who challenge you, teach you, and push you to be your best self,” Gates reminded them to think of others, especially the less fortunate. He wrote that it had taken him decades to learn about the world’s worst inequities and described this lack of early understanding as his one big regret.

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“You know more than I did when I was your age,” he wrote. “You can start fighting inequity, whether down the street or around the world, sooner.”

He finished by asking graduates to consider the progress humanity has already made, saying that he believes the world is getting better. “That matters because if you think the world is getting better, you want to spread the progress to more people and places.”