When workers do not find their assignments challenging, they become bored and so achieve less than their abilities would allow. On the other hand, when workers find their assignments too difficult, they give up and so again achieve less than what they are capable of achieving. It is, ttherefore, clear that no worker' s full potential will ever be realized. Which one of the following is an error of reasoning contained in the argument? ['assuming without warrant that a situation allows only two possibilities', 'depending on the ambiguous use of a key term', 'mistakenly equating what is actual and what is merely possible', 'relying on subjective rather than objective evidence']