Corporate earnings growth has long been one of the most important drivers of market returns, and has been fundamental to the record bull run.
"Markets rise and fall on two things: earnings and valuations. If earnings go up (other things being equal), so should stock prices," Brad McMillan, chief investment officer at Commonwealth Financial Network, said in a Friday note.
Profits have grown in 10 of 16 quarters since 2016. That's also supported valuations, as the ratio of price-to-earnings (P/E) is a popular way to measure company worth. When profits are growing, the denominator in the equation rises, which can shrink or control P/E and encourage investors to buy.