You may sell your BTC during the bullish period of, which may be a sign of good business. Now you bought again at the time of low market, here you stayed with Bitcoin and increased the profit margin.
At first I will say that I don't think we are discussing much about selling here but investing and your expression gave an insight of a trading strategy rather than investing making it off topic, buying low and selling high is more like gambling than investing. However when you sell at the time of bullish and planning to buy back when in bearish might make you waiting for too long before entering the market and you buy higher than your selling point, attempting to time the market can be very wrong approach because Bitcoin may go up and never return back to your speculated bearish season and you may completely missed out of the market.