If during the first year on an investment you lost 30%, then it would take a 43% gain the following year just to get you back to even. Remember once you retire the chances are high you will no longer be contributing to your accounts, and may be taking distributions from them instead.
Be sure your strategy for diversification changes after retirement to reflect you have transitioned from an asset accumulation stage of life to an asset preservation and cash flow phase of life. What may have been a good investment strategy during your working years may not be the best strategy for your retirement years.
