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.
In today's bitcoin, we know that if you invest with your spare money you may never make any fortune from bitcoin.
I think this advise is true for today also because spare money means that you don't need this amount for your daily expenses and if one put money that is not a spare amount so it will be sometime risky because of the need in householding activities.
Making fortune is necessary but if a person is hardly fulfil his family expenses then there is no need of investment and other thing is that person will only invest what he can afford so it does not matter that with little amount he make his fortune late or with large amount of money he make his fortune soon.