I agree with what you said, we shouldn't invest in what we don't know anything about, DYOR and know whether it'll be profitable or not. In Bitcoin investment you can know about it but the knowledge is not enough for you to invest in it, you need to have a steady source of income. People who are struggling to make ends meet, the unemployed should forgo the thoughts of holding Bitcoin, they should try and increase their income before accumulating it.
You don't need to understand everything about Bitcoin before you can have enough belief in Bitcoin for starting your investment.
You don't need to have to big capital to start.
You don't need to have top solid source of income to invest.
It is better if you have these things that support your investment but if you don't have them, you can still invest, it is just harder and more challenging for you to handle your finance, spending for survival and investment at the same time.
You need to hold Bitcoin for a long term before you can get ROI, except you buy during bull run, the longer you hodl the more profit it accrues to you on the long term.
Holding bitcoin for few years is key to have good ROI especially holding from two market cycles and longer.