Question

which thought pained the narrator and why​

Answer 1

Answer:

The “painful thought” that haunts the narrator in “My Lost Dollar” is that if Todd owes him a dollar and has forgotten it, it is possible, indeed it is theoretically probable, that there must be men to whom the narrator owes a dollar which he has forgotten. ... That is why he likes to remain forgetful of all those dollars

Answer 2

Answer:

The “painful thought” that haunts the narrator in “My Lost Dollar” is that if Todd owes him a dollar and has forgotten it, it is possible, indeed it is theoretically probable, that there must be men to whom the narrator owes a dollar which he has forgotten. ... That is why he likes to remain forgetful of all those dollars.