The ranks of the unemployed are filled with people of all ages and all levels of education 

who believed that, if you work hard, you will be successful. They never could have envisioned the day when their skills would become obsolete or their jobs would be sent to another country where the overhead is lower. They may very well have listened to the advice presented in the original claim when they were going off to college. With visions of dollar signs filling their heads, they enrolled in programs that guaranteed employment post-graduation. They were simply being practical. Therefore, students should not pick their undergraduate majors based on the careers available at that moment, because there is no guarantee that those careers will still be available once they graduate.

请问文中claim怎么理解？