I agree with you, all your Bitcoin investment shouldn't be sold at once. At least, a small fraction should be left to continue the accumulation process because as the days go by, the worth of Bitcoin increases, we are having more investors learning and adopting Bitcoin, and the most important part is the limited supply of coins to be mined which will in turn increase the value. Using the DCA strategy to accumulate would be a great a idea as it won't create any turbulence in your financial activities. All the person needs is a source of income to keep the process going.
The accumulation process should be long and the selling process should also be longer because if you sell all your Bitcoin at once then you will wait for another dip to buy again therefore keeping some and selling some for profit is a better idea which should be accepted by every individual.
Buying the DIP is a good approach but that doesn't mean that everyone who wish to invest in Bitcoin must first wait for a DIP before he buys, there are other accumulation methods that can guarantee your long-term profitability, such as the DCA strategy. This strategy doesn't require to try to time the market by making you wait for a DIP or believe that it's the best right/best time to buy.
Since one has a stable income, you could set an interval, weekly or monthly to buy and accumulate with a particular percentage of your income, and you'll end up accumulating a good number of Bitcoin without feeling the impact.
It's just saving money in a piggy bank.