Your discretionary Income is what you will use in buying bitcoin if you don't use your discretionary Income in buying bitcoin that means that you will be selling out your bitcoin anytime soon because when you use money which you are not supposed to use in buying bitcoin what you are indirectly doing is trading because you are using money for family up keeping to be buying bitcoin where as you are suppose to use your discretionary Income which is to be your left over money you will surely sell out when the need for family up keeping comes up you will have no choice than to sell to settle your press needs.