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Aggressive might mean forcing yourself to buy an uncharacteristic amount, so there's a bit of a push to buy a larger amount. But I agree with you that if the benchmark is discretionary funds then that means we buy according to our own ability, and if the situation is that these discretionary funds are increasing then increasing the amount of purchase is the right choice. With your explanation, it is true and I understand it, and maybe what is meant by aggressive here is buying more than we can afford so that it damages the cash flow. In making decisions, it's good that we have to consider it first, not until when we get a moment that is indeed profitable and we make decisions without consideration.
You seem to be mixing up aggressive with overaggressive @Jody.Drummer, since if you overdo it then you are either going beyond your discretionary funds or you are going beyond what you can psychologically tolerate, even though it might still be within discretionary funds.
Let's say that on average every week you have $100 of discretionary funds that are available for you to do whatever you want with them, and so you could choose to invest anywhere between $0 and $100 into bitcoin, and that is your choice regarding how aggressive or how whimpy you choose to be. Aggressive or whimpy are relative terms since $80 per week would be more aggressive than $20 per week, and $20 per week would be more whimpy than $80 per week, and at the same time, in the end the choice is totally up to you regarding how high or how low you want to go, and each week you could choose a different amount that you feel that you want to do that week.
You could also create a rule for yourself that you can choose to obey or not, and let's say that you create a rule that no matter what you are going to buy at least 20% of your discretionary income in bitcoin, whether that is whimpy or not.. That is your choice of how much you want to do... and maybe after 14 weeks of investing 20% of your discretionary income into bitcoin, you might decide to change your amount. Of course, with your discretionary income, you can also choose to save and/or you can choose to discretionarily consume. Personally, I think it is best to not ignore any of the categories of how you could spend your discretionary funds, even though you could have some weeks that you are allocating 0% to any of the categories, even if you considered each of the categories.