Originally a fish in the Mississippi River that migrated south in the winter. Term was then applied in the 1830's to lead miners from Missouri. Northern miners without houses who stayed for the winter lived underground and were nicknamed Badgers and Gophers. Southerners who would go south each winter were called suckers like the fish. They would return each spring to buy worthless mining claims. Hence the term was coined. This is also why Missouri is now the show-me-state.
Seeing good that was never really there in someone isn't being a sucker, and it isn't weakness.
The guy felt like a sucker, but he wasn't a sucker. Foolish is someone who thinks kindness is passive and weak. An unkind person doesn't change into a kind person, peopledon't really ever change. They are who they were when they were born.