Alice Schroeder, who wrote a popular biography on Warren Buffett, spoke to Business Insider about his life and legacy amid news of his resignation.

Warren Buffett shook the investment world on Saturday with four words: "The time has arrived." At 94, Buffett's pronouncement that he step back from CEO duties — which he will recommend to the board in a meeting set for Sunday — is less a shock than a matter of necessity.

Warren Buffett shared big news at the Berkshire Hathaway shareholders meeting yesterday: His plan to step aside as CEO later this year in favor of his longtime heir apparent, Greg Abel. If the announcement was huge, the timing was even more masterful.