Do our beliefs cause anything? Does a pessimistic outlook cause depression? If only I thought happy thoughts, then would my depression lift? Or are depressive tendencies primary and the pessimistic outlook a consequence of a predisposition? Can this underlying predisposition be changed or at least mitigated? Is what I am calling "an underlying predisposition" better called by the old term "character"? Are there aspects of personality that are unchanging in spite of the vicissitudes of circumstance? And if there are unchanging elements to a personality, would it be possible to know what they are with any degree of certainty?
Before I get ahead of myself, what do I mean by character? It might clarify a little to substitute "limitation" for character. A person has his/her own typical limitations. These can be repetition of the same types of mistakes. A person can have certain beliefs and value judgements that are difficult, if not impossible, to evaluate objectively and with detachment. A belief that women are (somehow) inherently trustworthy for instance. This line of thought strongly suggests that what is often understood as neurosis (doing the same thing over & over but expecting a different result each time) is in some cases at least a matter of character. For what it's worth, there is nothing in the concept of character that requires it to refer exclusively to uplifting moral qualities. Traditionally, along with good upstanding character there were also low and mean characters.
The argument against character is that of what I call eternal optimism. There are no limitations to one's personality, only resignation and not trying hard enough. This brings us back to what my colleague told me. Some mental states, if not all mental states, are causative. They make other things happen, even if only other mental states. Certainly it is the case that mental states seem to engender other mental states. For many people the feeling of certainty that comes with the repetition of the Lord's Prayer brings feelings of peace, calmness, and safety, just as the thought of homosexual acts bring feelings of anger, fear, and loathing to some of these same people. It is also seems likely that there is not any mental state that will engender the same mental state(s) in all people. It does seem that particular mental states in similar circumstances will typically in a given person give rise to the same mental states.
It is tempting here to follow the chain of concepts and reduce mental life to a species of mechanistic determinism. While I can't decisively refute faith in the causal nature of one's thoughts and feelings, I can offer an observation. Thoughts do not come on command. Thoughts and insights come without warning and when they are good and ready. Further we learn from our past, maybe not as efficiently as we would like sometimes. A given thought will often engender the same thought(s), but eventually boredom sets in. Otherwise, a person becomes boring and prone to repetition of the same old tired syllogisms and arguments.
Where do these reflections leave self-knowledge?