Equity markets have trended upward historically, even though there have been long stretches of flat returns. After the Great Depression in the 1930s, markets moved sideways for years. The same thing happened between 1999 and 2009 after the dot-com bubble burst and the 2008 financial crisis.
But even with these periods, it's widely accepted that stocks rise over time. In short, when it comes to bull markets vs bear markets, the bulls win.
