Regardless whether you invest on an amount you can or cannot afford to lose, the most important thing is, you are investing into bitcoin. There is higher possibility to gain rather than losing as much as bitcoin is concerned.
If you are planning to hold bitcoin for long term investment, their their is possibility of making profits rather than losing, but if you are planning to hold for a short period of time, then I wont guarantee profit within a short period of time. Even if you are planning to hold for a long term, then make sure you invest in bitcoin, and make sure you still invest any amount you can afford to lose, dont be carried away with current bitcoin market.
However, if you mean to say investing in altcoins, thats where one should stick to invest only on an amount you are comfortable of losing. Altcoins are just pump and dump scenario. And sometimes, once the correction lead to its dips, some altcoins can no longer recover anymore, thats the high risk investing with altcoins.
Both bitcoin and altcoin, you have to stick to investing with any amount of money you can afford to lose. Anything can happen to your investment at any most, have seen people commit suicide after losing money from their investment, and things like that doesnt make sense, to avoid any problem, just invest any amount you can afford to lose, and make sure your investment is in bitcoin.