Why did bob ewell attack jem and scout? why does atticus misread the signs that bob ewell might try to hurt him or his family?

Atticus was more surprised than anyone present when Sheriff Tate reported that Bob Ewell was responsible for the attack on Jem and Scout. Atticus never actually expected Ewell to harm his children; however, he figured Ewell might eventually come looking for him. He knew that Ewell was unpredictable and full of hate. And more than that, "He was out of his mind," said Atticus. Sheriff Tate thought differently, calling Ewell a "low-down skunk." Atticus shook his head. "I still can't conveive of a man who'd--"

" ... I thought he got it all out of him the day he threatened me. Even if he hadn't, I thought he'd come after me."Sheriff Tate was certainly more accurate about Ewell's character. Atticus, as usual, was willing to look on the good side of human kind, thinking even Bob Ewell wasn't evil enough to attack children.