“The Elements of Investing” by Charles Ellis and Burton Malkiel
If you want to understand why I believe the best way to invest is to create a low-cost portfolio made up of well-run index funds with a good track record and that’s properly diversified, then rebalance once a year, please read this book. The authors (as well as I) believe in the KISS strategy of investing and have the data to back it up. It's not a long book and can probably be read in just a few hours.
Read this book if you want a primer on investing, and how to create a strategy for maximized success!