The reason why some investors fail while using the DCA is improper planning because I see no reason why an investor that have engaged in a lot of investment strategies would not know that before choosing to DCA they need a stable atmosphere that will not deprive them of their continuous accumulation therefore having a reliable source of income and possibly alternative means should in a case where the principal source isn't coming forth again, they can eventually fall back to the alternative means to still continue forwarding the DCA.
You are right! Why should a man go to DCA if his income is not right. A person can think of keeping his money in a safe place only when he has a consistent income arrangement. And if he is sitting in the gallery waiting for the bull run to break his target after buying Bitcoin on DIP, then he is living in a fool's kingdom.
You must not have consistent income become applying the DCA method. Even if you are contractor whose income comes only when you have a contract, @JayJuanGee explained in an earlier comment that such a person can still make projections with the bulk money received upon execution of a contract and should have already figured out, as an estimate, when he will likely have another contract or cashflow. For instance, if he receives lump sum of $10k upon completion of a contract and it happens that from past data he is sure able to secure contract 3-4 times per annum, he can set aside $3k from this amount for 3-4 months DCA, that is if the balance of $5k is able to meet his needs for the time period and also remain like $2k for emergency spending. The point is that DCA must not be applied by individuals with regular incomes, even those with incomes that are not regular can apply the DCA method.