I don't think our emergency and reserve funds should come from our discretionary rather our discretionary is always used for Investing regular using the DCA depending on the method an investor chooses and then for front loading or for aggressive purchase when there is Dip.
You are supposed to build out your emergency fund and other variances of backup funds from a part of your discretionary income. Sim_Card is right because if you invest all your discretionary income into bitcoin and fail to build out your backup funds properly alongside your accumulating bitcoin, you run at a risk of tampering with your portfolio when the needs that would've been solved by your backup funds arises.
If there is an emergency and you do not have an emergency fund to sort it out, what would you do? Of course you would be left with no other option than to tamper with your portfolio in order to solve it and that is a bad approach to investing into bitcoin.
Again investing aggressively with your discretionary income without building your backup funds can best be described as being over aggressive and this can harm your bitcoin portfolio and stagnant your accumulation journey on the long-run because it would definitely prove unsustainable.