This is more than true, if you want to hold a little amount of money (less than $500) into an exchange to take the opportunities to buy some coins, just hold it on strong exchanges like Binance or Bittrex, otherwise, just stick to have it on your wallet
To get a profit, don't HODL for too long, because prices continue to fluctuate, so play as a trader, buy when the price goes down for a while and then sell when prices rise. Maybe the increase isn't much, but it's pretty good. Then repeat again like that so that the dynamics of bitcoin are more pronounced and become smarter to analyze the rise or fall of bitcoin prices.