New Delhi, Feb. 28 -- Annual reports are generally not known to be candid. It's a different story when you're reading Warren Buffett's annual letter to shareholders of his company Berkshire Hathaway. The billionaire investor mentioned the word 'mistake' 16 times in the last four letters-remarkable for a corporate leader, as admissions of error are often avoided in big companies.

"Sometimes I've made mistakes in assessing the future economics of a business I've purchased for Berkshire - each a case of capital allocation gone wrong. That happens with both judgments about marketable equities - we view these as partial ownership of businesses - and the 100% acquisitions of companies," he wrote in his letter to shareholders on 22 February.

I...