“Just because you can doesn't mean you should.”
Your brother has made a lot of money on the stock market and says that he wants to use some of the money to buy an expensive sports car. You try to talk him out of it (convince him not to do it) but he says he can afford to buy it because he has enough money. You say this because you still think the idea is dumb.
Just because you can doesn't mean you should.
This is a common English saying that means that there are some things that you should not do, even if you are able to do them.
This phrase is usually used to give advice to someone who's using their money, power, or skill in a way that's not very wise.
You can use the phrase just as it is to respond to someone when they say they can do something:
A: I can go all day without eating anything.
B: Just because you can, doesn't mean you should.
Or you can include the actions that you can and shouldn't do, like in the example at top.