The 4% rule originated from a study conducted at Trinity University in the 90s. Prior to this study, financial advisors recommended a withdrawal rate equal to the portfolio's average returns. However, this approach does not account for sequence of returns risk. The study examined 30-year rolling periods from 1927 to the present, and found that if retirees withdraw about 4% of their portfolio annually, adjusted for inflation, their portfolio is very likely to last at least 30 years. Even in the face of market downturns like the dot-com crash, global financial crisis, or the Great Depression, the 4% rule offers a high probability of not running out of money in retirement. The rule can also be used to estimate the amount needed for retirement, which is approximately 25 times annual spending. Although many retirees do not strictly adhere to the 4% rule, preferring an adjust-as-you-go strategy, it has proven successful for some, such as Taylor Laramore, who retired in 1980 on a million-dollar portfolio.