In all honesty a really good trainer cannot read a dogs' mind or always identify the motivation behind a behavior. However, really good trainers can read body language, tease out what is reinforcing about a particular behavior the dog engages in. Example: I can't tell you that your dog is really trying to dominate you when he greets you by putting his paws up on your belly. What I can tell you are the observeable things; your dog jumps up on you whenever you return home from an extended absence. I may also observe that you look lovingly into his eyes, greet him verbally and with physical touch. From this scenario I can extrapolate that to the best of my observation the dog is being positively reinforced for jumping on you. What do we know about positive reinforcement? From science we do know that R+ increases probabilities. By definition R+ means that a behavior that is reinforced will increase in frequency.