expected him to be rational and therefore not attack when he was bound to lose eventually

But that could have been his strategy...

when he was bound to lose eventually

Judging by Churchill's writings the loose eventually thing was far from sure at certain times in the war, though you might be talking about very specific episodes. I also came away with an impression from Churchill that Hitler consciously acted contrary to "rational" expectations. Though I cannot support it with a quote, I believe that Churchill was (rightly) credited with early insights about Hitler's danger because he picked up on this strategy and was able to see that it would work on the civilized Europeans.