Warren Buffett: Should you buy Index Funds at All-Time Highs?

When Warren Buffett speaks, I listen. But there's one thing he's never explicitly covered. Whether passive investors should pause their ETF and index fund purchases in wildly overvalued markets. Over the past year, we've seen the S&P 500 continue to push to new all-time highs. But does this mean passive investors should wait to see if the market cools off?