In my own interpretation about this slogan. The money that you can afford to lose is not necessary an extra money. It can be part of your savings that you can accept if it's loss like 10% of your savings more or less. I have my life savings too and I can lose part of it on investment since the money is just stored in my bank.
I don't know when will I die so I always using part of it on investment then leave the majority percentage untouched.
My experience tells me that Bitcoin fixed investment is a good investment method. In fact, in 3-5 years, the investment income is far greater than other investment methods. I always believe in the cyclicality of Bitcoin, and I know very clearly that the secondary market and leveraged contracts of centralized exchanges cannot be touched. I wouldn't be around someone who made a lot of money to be jealous of others.