Up to a point that's correct, but not substantially so.<p>Index funds are typically managed (for a very low fee) in such a way that they track the market. That means that to lose <i>all</i> your money the entire market has to completely collapse to $0, which hasn't yet happened and probably won't.<p>This is different from investing in a single company (or indeed in a house) - single company stocks have frequently reached $0, and houses can get caught up in natural disasters. Gold melts, paper money burns, people die, startups fail... but the weighted average of the market only suffers from a little bit of irrationality every now and again.<p><i>EDIT</i>: It's also possible that the company managing the tracker could go bust and/or make a huge mistake. That did happened to one UK index fund and cost the participants about 10% of their accumulated capital. Spreading money around is the only way to limit your losses when the universe decides to hand you a truck full of bad luck.