<prompt> Human: My uncle stopped contributing to his 401K shortly before the stock market drama a few years ago. Now, in light of some world events, hes resuming it, with 100 going to the S P 500 fund option.Hes telling everybody in the family that we should do that, too, but I read somewhere that if youre under 30 you should put at least 50 in the stable value fund. Full disclosure: Im not 100 sure I understand even 50 of what any of this stuff means. Im assuming the S P 500 means the hugest companies. But why would that be only good for older people? He says thats the only one to bother with because it goes up the most if you keep up with the news and time it right.Whos right? Cranky old uncle or the magazine article? Neither?  <response>: Most peoples uncles know little about investing, including yours. Probably not your best source of expert advice. Too bad he tried to time the market - he missed out on some amazing gains. And pity hes concentrating his risk in US large cap stocks - he needs global equities, as well as plenty of fixed income. You need to educate yourself. The Bogleheads Guide to Investing is a good place to start. 