If you decide to spend it on self and pleasure, you get to enjoy it now and find out in the next 10-20 years or so, you have nothing solid in terms of finance or investments. But on the other hand, if you decide to invest some fraction of the same discretionary funds in Bitcoin, while still grabing little fun, at a long run, you must have saved or invested something tangible if your investment lasted for years(let's say 4-10 years or more).
Agree with you to say that spending our discretionary funds in something that can't add any value to our life does not make any sense, I know that everyone is entitled to use thier discretionary funds whichever way they like But, those that have plans in the future will never use thier discretionary funds in something that will become a liability to them. but they will want to invest into bitcoin no matter how small it is because they believe that if they keep doing it consistently that they can be able to stack enough bitcoin in the future, But these is not going to deprive them from not having fun of course they will still have fun While making thier bitcoin investment rather they will just map out a little portion of their discretionary funds to get that which their heart desired for.