Given that I have already concluded that my colleague is irrational, I cannot trust him to make a rational decision regarding the choice of drugs. Thus I just need to make the choice that will save at least 5,000 lives. (Note: I cannot predict which decision he will make, since irrational reasoning can lead to either choice. But if he chooses the malaria drugs, then all for the better.)

Is it a common belief that someone who has acted irrationally with regards to X is unable to act rationally with regards to Y? I am not challenging, just pinging for more information because this came as a surprise.