And vice versa. So if you own big and little companies in you portfolio, over the long-term, things will more than balance out in your favor. Little US stocks. Big foreign stocks. Divide your portfolio into three and put a third in each.
Mutual funds are best.
While the stock market is where you want to be, most people don't have the discipline and commitment needed to learn to be good stock pickers. It's not that it's hard, but you have to study and learn the art of research and analyzing stocks, which takes time and practice. That leaves mutual funds as the investment of choice. Index funds improve your odds of success. If you can't index, then be cheap.