That was the case for me when I made Angel, which was in English and was a big flop.

A period of transition to a new quality in all spheres of society's life is accompanied by painful phenomena. When we were initiating perestroika we failed to properly assess and foresee everything. Our society turned out to be hard to move off the ground, not ready for major changes which affect people's vital interests and make them leave behind everything to which they had become accustomed over many years. In the beginning we imprudently generated great expectations, without taking into account the fact that it takes time for people to realize that all have to live and work differently, to stop expecting that new life would be given from above.

But in 2007, the music stopped. We had lost sight of our shared purpose and our guiding principles, in which growth and success began to cover up mistakes and a disease set into Starbucks. That disease, hubris. We lost our way and believe it or not, we almost lost the entire company.

My first mistake, of course, was in buying control of Berkshire. Though I knew its business - textile manufacturing - to be unpromising, I was enticed to buy because the price looked cheap. Stock purchases of that kind had proved reasonably rewarding in my early years, though by the time Berkshire came along in 1965 I was becoming aware that the strategy was not ideal. If you buy a stock at a sufficiently low price, there will usually be some hiccup in the fortunes of the business that gives you a chance to unload at a decent profit, even though the long-term performance of the business may be terrible. I call this the "cigar butt" approach to investing. A cigar butt found on the street that has only one puff left in it may not offer much of a smoke, but the "bargain purchase" will make that puff all profit. Unless you are a liquidator, that kind of approach to buying businesses is foolish.

So given a Time Turner, I would tell my 21-year-old self that personal happiness lies in knowing that life is not a check-list of acquisition or achievement. Your qualifications, your CV, are not your life, though you will meet many people of my age and older who confuse the two. Life is difficult, and complicated, and beyond anyone’s total control, and the humility to know that will enable you to survive its vicissitudes.

The friends with whom I sat on graduation day have been my friends for life. They are my children’s godparents, the people to whom I’ve been able to turn in times of trouble, people who have been kind enough not to sue me when I took their names for Death Eaters.