Why is the S&P 500 gaining amid the macro headwinds?

Why is the S&P 500 gaining amid the macro headwinds? The S&P 500 seems almost invincible these days, standing strong in the face of a slowing economy, weaker earnings, high valuations, a trade war, and rising Middle East tensions. Why are investors still bullish through all these obstacles? The Financial Times (watch, runtime: 04:00) gives a three-letter explanation: Fed. The US Federal Reserve maintained a slack monetary policy and low rates through the entirety of the previous decade, and this makes investors optimistic that the stock market will continue to go up.