I hope that he wont do that because I have read some newbies that did invest and did the wrong decision of investing what they cant afford to lose. And when they are in need of money, they were forced to sell the bitcoins that they have bought. While the situation of the market was unfavorable, instead of making a profit, they have made a lost that they have regret. That is why you are right that he shouldn't invest all that he has got.
Investing according to our respective abilities is wise enough in any condition because everyone will never disturb what they have invested when they suddenly need money in their own lives. So that the investment will continue without any obstacles or sell immediately when you need money, but beginners who often make wrong decisions when investing can also learn by themselves through the wrong method so that they can have the right mindset with their next investment in the future by not using all the money just for investment.