Final answer:
Learned helplessness is demonstrated by a client who, after years of unsuccessful attempts, does not believe they can lose weight, showing a state of perceived powerlessness.
Step-by-step explanation:
The concept of learned helplessness refers to the state in which an individual experiences a sense of powerlessness and consequently gives up trying to influence or change their situation, often leading to passivity and depression. Among the given options, the BEST example of learned helplessness would be a client who does not believe he will lose weight because he has tried unsuccessfully for many years. This example directly reflects the situation where an individual perceives their efforts as futile and has resigned to a state of helplessness over their ability to change the outcome.