I am sure that if someone starts investing from discretionary income and he creates a backup fund to do it regularly he will be able to easily pull accordingly that you say.
There are ways that it can be easy, yet usually it is not easy - especially since bitcoin tends to be so volatile, and if you are committing value to bitcoin, then even if the amounts seem small, they start to add up and they tempt you into selling too much too early.
If you are poor, and you never had much investment, even after 4-6 years, you might start to get tempted to tap into your bitcoin investment, and you may well get tempted to tap into it earlier than 4 years, and generally guys end up making mistakes of stopping their adding to their investment too early and also selling way too much too soon. It is not easy, and you don't even have to be poor to make those kinds of mistakes.
Among them, there are some poor people who are not qualified to invest and their income is so low that they are confused in determining their future course of action or will be behind in investing. But for mentally enterprising people, no obstacle can stop them from investing. After a break of some time or a few more years, he continues to invest Bitcoin continuously to fulfill his goal.