When to short is simple - when the price action AND other factors start acting bearishly. That is all you need to focus on.
The common mistake is to short when other factors are bearish but the price action isn't - or, worse, when the price action is bullish. That is how you get screwed.
Think about it - when do the biggest, fastest price declines happen? In bear markets, or in crashes after parabolic blowoff tops. They don't happen in grinding bull markets or during the blowoff process. So it is insanity to position yourself short in those 2 conditions.
The common mistake is to short when other factors are bearish but the price action isn't - or, worse, when the price action is bullish. That is how you get screwed.
Think about it - when do the biggest, fastest price declines happen? In bear markets, or in crashes after parabolic blowoff tops. They don't happen in grinding bull markets or during the blowoff process. So it is insanity to position yourself short in those 2 conditions.