1. Invest in Bitcoin with your spare money:
I can say that this advice is not necessary in today's bitcoin world. This advice was only relevant like a decade ago when bitcoin was been seen with alot of skepticism. Some saw bitcoin as gambling, some saw it as a ponze scheme while others saw it as a bubble the will burst.
Have you forgotten that we do have bear markets that last a while?
Investing with spare money means in case of a bear market, one won't be forced to sell of there bitcoins at a lower market price just because they have to cover other expenses. Same applies to one investing what they can afford to lose. Nothing is obsolete
In today's bitcoin, we know that if you invest with your spare money you may never make any fortune from bitcoin.
But Bitcoin can still go x2 to even x7 in a bull market. How many investment options can do that in 3-4 years?