Let it be known that I am not a fan of psychology. Mostly because, although I can understand it on a rational level, applying it on a day-by-day basis is much too tiring for someone like me.
On the other hand, I do very much enjoy studying animal behaviour. Unlike humans, their rationale is often much more straight forward and easier to interpret - given you understand their biology, of course.
Most people are somewhat familiar with canine and feline behaviour. However, herptiles and other exotics can be much harder to interpret for the average Joe. This is the reason why researching your pet-to-be is so important. Some reptiles can live up to 20 years in captivity if cared for properly. A key part of their survival, however, depends on their humans' abilities to accurately interpret their behaviour. Sometimes, the signs that something is wrong are so subtle that most people wouldn't notice them.
To a certain extent, mammals - even exotics - are easier for humans to understand. There is a certain level of familiarity to their behaviour that we can identify with. The same cannot usually be applied to reptiles, for example. Apart from their natural survival instinct, which applies to most living beings, their reaction and outwards demonstration of illness, for instance, can greatly differ from ourselves. This means that in order to care for them properly, one must first familiarise themselves with their behaviour in the wild, their diet, their basic anatomy and even their history from an evolutionary stand point.
That being said, one thing I have come to appreciate is the importance of observing your reptile for their individual 'tell-tale' behavioural traits. What I mean by that is that I believe that animals have certain behavioural traits that are due to their individual personality. The more I observe my bearded dragon, the more familiar I become with the way he reacts to different situations. Small signs such as the position of his tail (or in his case his stump), the area of the vivarium that he will choose to rest, the times of the day that he will chose to 'go to bed', etc.
Getting to know your individual pet to this level of detail will not only result in a likely much more involved relationship between you and your pet but it may also mean the difference between life and death for them. Reptiles are notorious for not showing outward signs of illnesses until it may be too late. Being able to identify extremely subtle signs that differ from an animal's normal behaviour may be a keeper's only chance at saving their animal's life.
For that reason, I would encourage any keeper to get to know their pets. Observe their usual behaviour and watch out for any signs of behavioural change. If you notice a difference but cannot put your finger on it, take them for a check-up. You would be surprised how often one's metaphorical 'gut feeling' gets it right.