Tesla stock fell slightly in early trading Thursday. Shares of the electric-vehicle maker were bouncing back after another tough week. First-quarter earnings are due in a few days. After that, investors should start thinking about China.

The day-to-day volatility for the S&P 500 settled down on Monday and Tuesday. But two-thirds of stocks in the U.S. large-cap benchmark index have declined this year, with 220 of the 500 stocks down at least 10% and 82 down at least 20%.

The market wreckage strewn by President Donald Trump’s trade war is uniquely driven by minute-by-minute policy whims. A trader riding out the tempest might look to the simple aphorisms passed down as time-tested investment wisdom for guidance.