By this point Helena's mental state was near collapse as she began to behave irrationally.

Failing in this, he/she may become frustrated and behave irrationally.

If others are with me, he might behave irrationally.

Even in this case, it is not required that every player guess 0, since they may expect each other to behave irrationally.

The people who make up markets can behave irrationally.

This is not to say that investors are behaving irrationally.

When he behaves irrationally it is necessary to be firm with him.

The stock market has been more volatile than usual, but that does not mean it is behaving irrationally.

But look what happens when these people behave irrationally.

The man had no reason to behave so irrationally.