If you think that your stock will come back in 5+ years you will probably have to think again. The companies for which you have the stocks may just go bankrupt and you will have no way of recovering the losses.
And that's where having a diversified stock portfolio comes in. If any 1, 5, 10, or 20 of the companies I've got stocks in go bankrupt, my stock portfolio can still recover, especially since it's spread across various sectors so if and when a single sector tanks it won't affect my whole stock portfolio. That's also where having a diversified overall portfolio comes in. Anyone who invests solely in stocks is an idiot. Ideally you should have a mix of stocks, bonds, cash, commodities, and real estate (for most people who own their homes, that's all the real estate investment that they should have - anything more and they're most likely over-exposing themselves).
Given that I won't be accessing my investments for many years (5 was an extremely low estimate - in fact I don't really plan to touch any of it for 15-20 years, with the possible exception of selling my home to buy another depending on if real estate prices in other locations drop more than in my location), the only way I'll be taking a serious dive is if absolutely everything tanks and we go back to a barter economy, in which case everyone will be in the same boat anyway.
All the people in the world screaming about how the sky is falling won't change the fact that wise investors plan for long-term economic disasters and, barring a complete collapse of the entire worldwide economy, can ride them out. And if a complete collapse of the entire worldwide economy does happen, then we're back to medieval times anyway, because modern society can't function without the global economy.