I think you are a little bit confuse here let me put you through investing what you can afford to loose is not an investing strategy rather it is an investing advice given to investors both New and old to invest in bitcoin with what they can afford to loose, because there no guarantee that your bitcoin investment will be successful so returns are not guarantee, since nobody knows what will become of bitcoin tomorrow, that is why it's advisable to invest what you can afford to loose in bitcoin.
It is one part of your investment strategy because you need to have something for cooking, here investing.
You can not invest if you don't have investment capital but how you get the investment capital is important. It's more important to know that what you have after you spend money for investment, like whether you have emergency fund, and at least enough fund for your spendings. It's about risk management of your finance in general and your investment capital in specific.
If you invest what you can not afford to lose or invest all money you have, you have bad financial management, terrible risk management, and they are all terrible parts of your investment. With two bad pieces in your investment strategy, you have lower chance to succeed with investment.