It's great advice...the challenge, though, is gauging the degree of fear or greed.
Right now, fear is strong. I suspect we're forming a base. On the other hand, the averages are still high if one is looking for those rare periods when stocks are truly cheap. One measure is earnings related to price, or price earnings ratio.
The chart
HERE is interesting. Take a look at the lower chart, the one that tracks P/E ratios.
As of the 10th of October, Friday, it was 18.31 according to Barron's. That still looks expensive, unless one expects very rapid growth in earnings.
Hard to say.