It is one of my favourite rules that I use in my common life, I just spend money to buy bitcoin or any other cryptocurrencies and I'm not regretting it because I can't that money has already spent.
Yes I agree on that, through investing we really need to select the most trusted and most profitable coin on the crypto feild because some other coin is really fake or scam and we don't have any assurance to earn on it. So I suggest to invest on common coin.