Steve Jobs once called Apple design chief Jony Ive his "spiritual partner," and the two execs had an incredibly close professional and personal relationship.

When Ive remembers his friend and co-worker four years after Jobs's death, what stands out is the ability he had to stay fully focused on whatever he was working on.

Ive says he never managed to achieve the same level of focus as Jobs, but a daily exercise helped him realize how satisfying it could be to say no.

Nearly every day, Jobs would ask Ive the same question.

"He would try to help me improve my focus by asking me, 'How many times did you say no today?'" Ive said on stage at the Vanity Fair New Establishment Summit.

In Jobs's opinion, the more noes the better. To have extreme, laser-like focus, Jobs was always willing to reject a lot of opportunities, even if they sounded great.

"The discipline to turn your back on something you believe in passionately, so you can apply yourself to what's at hand, is really remarkable," Ive said. "It's a deeply uncomfortable but really effective thing to do. It's more than a practice, it's more than a habit ... it's a really wonderful ability."

Ive was humble about his level of focus compared with Jobs's, but Jobs once said Ive was "the most focused human being I've come across."

Ive also talked about his new job and the stress of the creation process.

"'Tortured' doesn't even begin to capture it," he said.

This story first appeared on Business Insider