15-20 uncorrelated investments (at any risk level) offer significantly better risk/return characteristics than a single investment. Also called the "Holy Grail of Investing".
Principles by Ray Dalio (page 56-57)
For a model portfolio of a Risk Parity strategy, refer to Reverse Engineering AQRs Risk Parity strategy
☝️ Watch this rare video (starting at 6:00) where Ray Dalio explains why he invests in at least 15 uncorrelated bets at each time.