(Depending on) what part of the cycle that the market is in can be a determinant of when to position in momentum / growth stocks or value stocks. "Factor crashes" are anomalies that affect the performance and total return of stocks falling under momentum factor and value factor when: 1) a rising bull or trending market cycle is present which favor momentum stocks ( expensive ) = value underperforms (sometime drastically) and 2) in the initial period following a severe bear market bottom = value outperforms and momentum has it's worst performance.