Only if you let them, Obi-Wan, or they are manipulated by an outside force. And even then, you should never expect to perfectly master your emotions.

[She gives him a grave look]

And emotion is rational, it is predictable, and one can learn what to expect from oneself in a situation if they experience emotion. By learning to control them you MAKE them rational. That was the meaning of Odan Urr's teaching.