> Curious if you have a source for that?

Some people think that we are facing secular stagnation, and the economic growth is slowing down. The avg federal reserve interest rates have been falling at 2% per decade for 5 decades, and signifies less growth in the economy. Sure, this low interest rates have actually fueled the stock market boom as the value of future earnings is high, but the growth is not sustainable. For one, we are going to end up with some stable p/e ratio, and the growth of stock market because of low interest rates will stop. And two, the interest rates will also stop going down as fast, as a rate of say -10% sounds pretty bad in what it means for the economy (negative growth of that magnitude), so people do not think we will have such a situation.