If you understand bitcoin really, then even if you pour all your money into bitcoin at once, and bitcoin price dumps, then they won’t panic. If you go in all into bitcoin, and you notice that their is a dump in bitcoin price, then you should know that as long as you can hold, then bitcoin price is going to bounce back. If you check bitcoin price history, then you should know that no matter how low bitcoin price goes, it’s going to bounce back even if it’s going to take time, so if you are investing, always have it in mind to hold for long term, and you don’t have to panic about anything.
Since Bitcoin has the tendency to increase overtime then there won't be any need to panic if one pour all their money into it and the price drops like you said, but then it's not advisable to do that you don't put all your money since there would still be other important daily needs that you'll settle that's why you'll use the discretionary funds mainly for such investment, if Bitcoin was an investment that one would embark on then make good gains in a short period then anyone can choose to do that but since Bitcoin is a long-term asset I don't support investing all your income at a particular time in it, that's why you have the DCA to invest in bits overtime, accumulate periodically.