Read here: https://www.retirewithpossibilities.com/dont-let-fear-of-the-unknown-throw-shade-on-your-retirement/
Rather than using this approach, you should start with the end in mind, figure out your appetite and comfort level with risk, set a target asset allocation and only at this point pick your funds.
To learn more please read our latest blog on the topic https://www.retirewithpossibilities.com/4-steps-to-take-now-to-make-your-401k-spring-back-to-life/