Retrievers were originally bred as hunting dogs.  Their job was to sit by the hunter and wait until game was shot and then retrieve it on command.  This often meant swimming through cold water or running through dense brush.  Labs were also taught not to damage the game upon returning it to their master.
Knowing what type of tasks the dogs were bred to perform assists us in analyzing what type of behaviour to expect from a breed.  In the case of labs, they are fairly insensitive to touch.  They readily leap into cold water and sit patiently in the cold in order to please their master.  Physically tough dogs, they are very tolerant with children …