How do you determine how much you are willing to lose? It seems to me that this initially implies small amounts for investment, but in this case you will not lose much, but your investments will not bring you much profit either. Therefore, I believe that this rule can be applied to altcoins when the risks for your investments are really very high.
Any reserve funds that have been invested in bitcoin are ready to lose for any risk, because there is no exact speculation on bitcoin price predictions and we still believe that our investment in bitcoin will not lose much if we position the investment for the long term. Some of the reserve funds have been allocated to invest in bitcoin, have nothing to do with other funds, we even have an emergency reserve fund for whenever we need it.
And then I have a counter question, if you only invest the money that you are not afraid to lose, what do you do with all the other money that you save, you just keep it?
We have financial management based on allocation and purpose, including funds for daily needs, some deposit funds at banks (fiat), reserve funds including investment funds into bitcoin and emergency funds, gold investments, everyone has different financial management, so it's clear that all other money is used according to the distribution of allocations that have been regulated in financial management.