If you don't need the money, wait to sell your bitcoins. Its possible that next year prices of bitcoin were bigger than now. (But it isn't 100% secure).
It is a good advice. Unless you are lacking money for you daily expenses then there is no reason to sell mined, or bought coins right away.
Always expect a bubble, for example yesterday bitcoins was worth $20 dollar less than it is worth today. In the long run this might be even bigger deal.
Well for me is a good advice I don't spend a lot of Bitcoin and money so I just save it.
And yes maybe today Bitcoin has increase but maybe tomorow will go down again.