Friends

Don't try and change other people's behaviours. They have decided to do what they do. The best way of changing someone's behaviour if you know it is in their best interests to do so, is to provide them information which will help them make a better decision.

Simply telling someone they are stupid, or that they cannot do something provides no justification to them. And it's likely to cause them to look for hypocritical scenarios.

Behavioural changes have to come from themselves.