Sympathy is often abused. Typically, a subject has been used or taken advantage of many times by a person or group of people appealing to the subject's sense of sympathy.
In some cases, the subject gets used by a singe person or group of people several times. In some cases, the subject is taken advantage of or used several times by different people or groups of people.
It may take one incident, or it may take many. Eventually, though, the subject becomes so jaded that when they actually come upon a person who may actually deserve sympathy, they have none to give.
In such cases, one is likely to hear the subject use a phrase similar to the following:
"If you're looking for sympathy, it's in the dictionary between shit and syphilis."