Bitcoin investment is risky just like any other investment but the risk is lesser and if you invested with a discretionary income, there is no need to think about the risk that is associated to it again since you can bear any aftermath of what comes out from your investment if things peradventure goes wrong
You thought wrongfully about it.
Invest what you can afford to lose is a very classic advice and by invest your discretionary income, you do your capital management better. Risk is risk and it is nearly the same for your investment capital, and if you picked a wrong cryptocurrency for investment, you will have same 80% loss of your initial investment capital. It's not matter that your initial capital is $100 or $1,000, it gives you same -80% ROI, that is insane and painful.
By having better financial and capital management, you control and reduce risk of things beyond your investment better. Like you never let your monthly spendings or emergency forcing you to sell your bitcoin at lost prices.