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[...] but what I'm saying in essence is that always use what you can afford to let go and while investing ensure to keep your reserve and emergency fund which is very necessary because it will help you scale through some unforseen circumstances and lastly discipline, patient and consistency is the key to a successful...
What you are saying is money management, of course money management is needed in any investment, not specifically for crypto. Allocating even 80% of your weekly/monthly income to bitcoin investment will not be a problem if you can live with the remaining 20%. Look at the price of bitcoin now, it is up than a few days ago. Proving that investing in bitcoin is definitely profitable (especially in the long term).
In essence I think what he's saying about investing with the amount any one can let go is because of the price movement of Bitcoin, it is not advisable for anyone to use all their life savings to invest in Bitcoin this does not mean that Bitcoin will disappoint you no this is important because the price may not be what you expect to see and to avoid panic and fear people are advised to invest with spare money and also don't depend solely on Bitcoin investment so that they will not regret when the price doesn't go up as expected.
The price of Bitcoin may have increased with time and since the declaration of Trump as the winner of US election there has been a massive increase in the price of Bitcoin thereby seeing Bitcoin move down 65k to 90k, the price is expected to hit 100k before the end of December but this is just the price prediction it may increase or go down with time.