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I don't know why it become wrong mindset maybe we have different mindset how to become profitable. If HODL is your ways to be profitable even the price is dropping I don't see any problem if you can wait for long.
People have different mindset that is why there's a panic sell because they can't handle the emotion during bear market.
Personally either I don’t see it as a bad mindset since the goal is definitely to have more bitcoin, but personally I think I understand OP ply and seriously I have studied this method and sincerely it is usually a bad strategy for me, reason been that the bitcoin market is heavily unpredictable in my opinion and you can’t predict the future.
Now let me make an example, if you sell bitcoin while it was pumping say at $100k like we are undergoing now with intention to buy back in the next dump for more bitcoin portion but rather the market then continues moving from this point till a much higher price level. With bitcoin price been unpredictable there is tendency that the lowest price we would see is bitcoin not coming back to $100k again so buying back again would now be in loss.
Selling a portion could be lessen the risk but one thing I usually say is when taking profit, simply take profit after a long term and not risking selling high to buy low immediately like you stated the market might caught you out