We all know Fredo wasn't the "smart" one when it came to mafia business but I don't think he was like retarded or anything. I mean if he felt that there was a threat to Mike's life he would have let Mike know. Even Mike who everybody thinks is the most clever mafia don ever didn't see it coming. I agree with Apple Fredo was the type of guy who wouldn't be able to sit at the dinner table with his mother knowing his brother was about to be whacked. He wouldn't be able to go out fishing with his nephew. I still don't belive Fredo ever wanted to be the Don. I think he just wanted to be a respected mobster. Fredo wasn't cut out to be a mobster but he was good at the casino business and things like that. If you are a smart mobster it doesn't mean you are smart in other areas of life.