From Warren Buffett
Don't view stocks as ticker symbols
To help maintain a clear head during stock market crashes, investors should remember that they are business owners -- not ticker symbol owners. While stock prices may plummet, the majority of companies with good business models and strong competitive advantages will likely see a far smaller negative impact to their underlying businesses during these periods. So, be sure to detach stock price performance from business performance.
Buffett elaborated on this concept in Berkshire's most recent shareholder letter:
"Charlie and I view the marketable common stocks that Berkshire owns as interests in businesses, not as ticker symbols to be bought or sold based on their 'chart' patterns, the ‘target' prices of analysts or the opinions of media pundits. Instead, we simply believe that if the businesses of the investees are successful (as we believe most will be) our investments will be successful as well."