"The father of value investing, Benjamin Graham, explained this...

"The father of value investing, Benjamin Graham, explained this concept by saying that in the short run, the market is like a voting machine--tallying up which firms are popular and unpopular. But in the long run, the market is like a weighing machine--assessing the substance of a company. The message is clear: What matters in the long run is a company's actual underlying business performance and not the investing public's fickle opinion about its prospects in the short run.
Over the long term, when companies perform well, their shares will do so, too. And when a company's business suffers, the stock will also suffer. "