Just as a sensible income is needed to start investing, 2 more things are needed
1 Basic knowledge about Bitcoin
2 Faith in Bitcoin
I wonder what type of sensible income you are talking about because to the best of my knowledge, their are so many guys out there that wish to invest in Bitcoin that are earning a sensible income as you called it but still can't figure out their discretionary income, what an investor need in other to invest in Bitcoin consistently is a discretionary income and the will to hold for a very long period of time, because if he has the will to hold for the future, he will put down measures that will make him develop a strong holding hands, like having an emergency and reserve funds in place to protect his investment against any unforseen circumstances that may arise in the future.
Very much outlined mate, having a sensible income will help to invest in Bitcoin but managing the sensible income well sharing is part by part and using the one that you can actually not be stressed with to invest in Bitcoin help investors a lot, don't want to called it discretionary income but in reality that's what it, you some people have to be taken down the lane for them to understand, some people failed in their Bitcoin journey not because they weren't capable of investing in it but consistent tampering of their investment led them to decide to withdraw all just because they keep using an amount that isn't comfortable for them, don't know that till this moment some people don't know that emergency funds is needed as a bitcoiner to battle some unexpected stuffs that may likely come along the line during ones Bitcoin accumulation and holding and this funds can be called a salvager of unexpected monetary situation it in turn helps us to battle any stumbling block on our way that may cause us to have the mindset of withdrawing prematurely.