Your dog jumps like a Kangaroo when you reach for the lead - this is learned behaviour. He sees the lead and believes it's necessary to bounce for you to put the leash on. This is because previously when you picked up the lead, he bounced and then you clipped it on. In other words, the bouncing is rewarded with a walk so the dog thinks jumping is something you want him to do. Learned behaviour is how Mother Nature programmed wolf cubs to learn. In its simplest form it's a way of keeping an inquisitive puppy safe. When he tests the boundaries and something nice happens, the pup is liable to repeat the action. Likewise, if something unpleasant happens, he's more respectful of it in the future. But learned behaviour can happen for subtle reasons, such as the dog who barks at those passing-by the front room window. In this case the dog's reward is that the people go away. They were only passing in the first instance but the dog believes his barking brought about the result he wanted. From barking to pulling on the leash, jumping up to running away, many of our dogs bad habits are learned behaviours. Now you have a better understanding of why things go wrong, you see there is hope that they can be corrected. Key to this is establishing a new, more appropriate link in the dog's mind. How easy or difficult retraining is depends on how well-established learned behaviour has become.