Of course predicting the future is impossible. But there’s a lot more than 40 years of data to support the buy-and-hold idea. The updated Trinity Study spans from 1925 to 2009, so includes the worst economic calamity in US history. It concludes an inflation-adjusted 4% withdrawal rate is safe for 30 years in 95% of historical 30 year periods. An inflation-adjusted 3% withdrawal rate succeeded in every 30-year period.