The world is a very big place, and we don't necessarily understand what we think we know. Along those lines:

What's the better way to invest—little by little, or all at once?, October 09, 2012, Vanguard, https://personal.vanguard.com/us/ins...eraging-102012

A Vanguard research paper issued in July 2012 found that the lump-sum approach has historically outperformed the dollar-cost method in the United States, United Kingdom, and Australia. But a close look at the study's underlying assumptions reinforces the idea that there are compelling arguments for both investing methods.