When the stock selloff began in earnest at the start of this month, it looked like a simple loss of momentum for a bunch of high-growth disruptive stocks that had risen too fast. Now it is morphing into broader concerns about the economy, and investors are factoring in less chance of the Federal Reserve raising interest rates aggressively next year.

The question on which investors need to take a stand: Is this a healthy correction in a bull market with further to run, a reset lower in belated recognition of this year’s geopolitical...