When you are using only your discretionary income to invest in Bitcoin it means you are investing with peace of mind. Even if Bitcoin falls, your life, bills, and responsibilities stay safe and intact, so use only your Discretionary income for Bitcoin investment or accumulation.
Remember there are set of people that invest From thier discretionary income yet they don't have peace of mind, they still panick during the dip. So this is just all about discipline, You can have a discretionary income to invest in but if you're not discipline you can't stay focused as you may be tempted to sell off your holdings some day due to pressure so as a newbie who is about getting started with bitcoin investment you need to be discipline. Discipline i mean in terms of sticking to your decision once you decide never to tempter your bitcoin investment for any reason then you Stick to the decision let your yes be yes not just after making a decision maybe due to pressure you just decided to sell your holdings no, you just need to stay discipline no matter what.