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.
If you use your entire money to invest in Bitcoin, then which money are you going to use for your personal upkeep? Does that mean anytime you need money, you should sell the Bitcoin you have stocked in your wallet? NO. That is why the advice to invest your spare money in Bitcoin is always good for new investors, so that they can buy Bitcoin with the aim of holding it for a long time.
2. Invest what you are able to lose;
I have a question!
Who has ever lost in bitcoin?
I agree with this since only those who lose patience and sell their Bitcoins lose money on their Bitcoin investment. However, the advice should be applicable to cryptocurrency investors as well.
3. DYOR (Do your own research):
This advice should be for altcoin investors. If I may ask, what kind of research is one, especially a newbie expected to make in bitcoin. Are they researching the road map of bitcoin or are they researching the developers behind it? The right thing is to know when to buy. Simply buy low and sell high.
This should also be applicable to all, in my opinion, because some new investors think that it is a get-rich-quick scheme where they will just put in their money and it will do 2x in a short period of time, but if they were able to do their research, they would understand how the Bitcoin market works.