Can somebody explain the logic behind the protagonist's naivete? Sure, he was abused and lied to in his previous party, but that doesn't explain his complete lack of common sense. For example, he claim to be the weakest, and he can carry 200kg, yet he doesn't find it weird that nobody else in the town carry 200kg worth of load? If he's the weakest, then everyone else must be able to carry more, yet nobody does.
Ai-chan doesn't understand how this misunderstanding can happen. Should it just be attributed to 'trash author doesn't know how to use logic'?