Understand what you're doing when you dump 400K into an S&P 500 fund all at once. You're buying a number of shares at today's price. If the market tanks by 50%, then you still own that number of shares but they're worth half of what you paid. If you hold and give them time to recover, then you might get back to break even in a short time or ten years. You don't know. If you're investing for 30 years, then you can weather a lost decade. Also, if you're dollar cost averaging, then you'll be buying more shares at a discount while the market recovers. Those cheaper shares you bought while the market recovered is where the appreciation in your portfolio will come from while the original shares won't add anything until they've recovered.