It is like someone calling you out and asking you if you can go out to a nice restaurant to eat. Usually, you spend between $3 to $15 for the ingredients and preparation costs of your regular meals, yet you know that if you go to the nice restaurant that is being suggested, it is going to cost you at least $50, and it might cost you even a bit more. So you have a question in your head about whether you have the $50 or not. If you do, then you have discretionary income that you could also choose to spend in bitcoin rather than going to that nice restaurant.
Yeah this could be another explanation of discretion. Being able to afford a meal of $50 or not is determined by your level of discretion. If a person often spend some bucks on food like 5-$10 and decide to have a nice and more decent meal for an outing depends on his discretion. He may chose to buy a meal of $50 or decide to invest it on bitcoin and go back home to eat his regular meal just being financially wise is the case. But If also he has a more decent amount in his discretion then he may well spend the $50 and yet not being affected by his regular investments. So the main point is that weather you chose to increase or decrease in our spending all
Depends in your discretion.
however this may be defeated if you lack management skill, some people have good discretionary income and still find it hard to accumulate because they don't manage there income very well why some set of people have small discretionary income but because they have good management skill they accumulate with ease, so knowing how to manage your discretion income will determine how far you will go in your Bitcoin investment journey.