Answer:
Soto develops the concept that poor people need to work hard until they are old and no longer have the strength to do so.
Step-by-step explanation:
You did not quote the book to which this question refers, but when researching it, I could find that you are referring to “One Last Time,” written by Gary Soto, where he reveals life as an immigrant and low-paid jobs that he and his family had to take to survive.
In lines 11-18 of the book, Soto shows the concept of working until forces run out. This is because, in these lines, he describes the work of his grandfather and grandmother, who had to face very heavy jobs in order to survive. They only stopped working when they were old and no longer had the strength to continue working.