Many people invest by borrowing money from others. If one has a fixed source of income he can borrow money from others and invest but does not have to sell his investment. Because people don't always have money even if they have a job. So if he invests with a loan and later if he can repay the loan with the money he gets from his job at the end of the month, it means he can easily repay the money he borrowed from others. As a result, he no longer has to sell the investment to repay the loan.
It is very wrong to borrow money to invest in bitcoin because things may not turn out the way you expected it to it will be better to invest with little amount according to the level of discretionary income using the DCA method which will enable you accumulate Bitcoin regularly it could every week or month instead of going borrow money to invest in bitcoin for a long time remember that Bitcoin investment is not what you will put your money now and expect to cash out in few weeks time so it will be more better you invest with money won't be needing for a longer time which could probably be 4-10 or more.
The first advice I would give you is to read my post very thoroughly. I may have mentioned that if you have a fixed source of income, you can also invest in debt without any problem. It means that suddenly we need more financial than necessary for very important work due to which we spend all our monthly earnings. So at that time we cannot buy bitcoins for investment. At that time if we borrow some money to buy regular investment then maybe our investment will not stop. Since we have a fixed source of income, we can repay the loan later with the money we earn from that source of income.