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You are right, as a poor person the process of building one's Bitcoin investment will take more time than expected especially when he has no emergency and other back up funds because he will start building those funds a long side with his or her Bitcoin investment and because his or her discretion income is small building those things together will take a very long time.
One thing that also prolong the journey for a poor man is excessive emergency issues when his having too much emergency issues it will be hard for him to build up except those emergencies are within the means of his discretion income if is not then it will be impossible for him to build up his Bitcoin because those emergencies will eat up all his back ups funds and his Bitcoin.
Part of the goal should be to build up back up cash so that he is not getting into emergency situations, and yeah, you are correct, that a guy with low discretionary income, he will constantly be fighting to figure out how to keep building his back up funds and his bitcoin and there may well be periods in which he is not able to buy bitcoin, and hopefully he can have systems in place so that he does not have to sell his bitcoin also... and yes.. not easy.. and each person has to figure out the extent to which he can even invest into bitcoin.. and if he has enough discretionary income to actually be able to invest in bitcoin.. including that if he is actually misclassifying his funds as discretionary when they are actually needed to be in his back up funds or his emergency funds because he already has cashflow issues that might relate to the amount of cash coming in being too low and/or the amount of his expenses being too high.
In the process of one trying to figure out if they can possibly invest in bitcoin it's paramount for one to first make decisions based on the what they most have gotten from examining their income using the 9 individual factors and no matter the level of poverty one can be able scale themselves based on how much they earn monthly or weekly and put in the necessary funds where they are supposed to be then before going into investing in bitcoin.
One major thing I think should be be considered most is emergency funds and once one have this emergency funds to cover for the length of 4-6 months I think one is good to go with the bitcoin invest hence whatever they may encounter on the journey would not cost them to sell their bitcoins. Additionally, it's very necessary for one to know the difference between each classification of funds hence to to complicate them or mistake them for one another.