Warren Buffett says he goes to bed more worried about another pandemic or nuclear war than his company

• Warren Buffett says he worries more about nuclear war or another pandemic than his own company.
• He told CNBC "I never go to bed worried about Berkshire" Hathaway as he can always change something. 
• Buffett's friends including Bill Gates partly credit his success to his optimism and self-confidence.

Warren Buffett said he worried more about the prospect of catastrophic global events than the success of his own company when he goes to bed at night.