Lifecycle Investing by Ian Ayres and Barry Nalebuff

This book tries to popularize taking riskier investments throughout life, with lots of risk early so as to provide a constant lifetime risk exposure.

You can't time the market. But you can time yourself. You know how many years you have till retirement and how much of your income you are likely to put aside during that time. You can use this self-knowledge to diversify your exposure to the market.

-- What If...