I've long believed that one of the most important aspects of rationality is learning to be skeptical even of your own rationality. Just like unquestioning faith in a creator or social movement is naive and usually incorrect, so is unquestioning faith in yourself and your own memories.
Most of us instinctively think of ourselves as rational, logical people. We believe that our thinking processes, assumptions and even automatic reactions are justified, proportionate and correct.
This is, to put it bluntly, wrong.
Over the last few decades cognitive science has demonstrated repeatedly that our "natural" way of thinking is actually little more than a collection of useful evolved heuristics, not a rational, logically-defensible framework. They've even collected a huge array of known cognitive bugs. We're all guilty of most of these biases much of the time, and even those of us who know about them and try aggressively to avoid them still fall prey to them upon occasion, often without even realising.
What it comes down to, broadly, is that you are not a reliable narrator, even of your own experiences, opinions and life-history. You are just as prone to biases, subconscious (and sometimes not-so subconscious) whitewashing and a whole suite of cognitive errors and biases as anyone else. Don't just gloss over that - let it sink in for a moment. Much of what you "remember" is invented detail. Many of the life-experiences that make up your sense of self and your identity are exaggerated, grossly biased or even wholly fallacious.
This is a revelation for some people, and for others (too attached to their mental image of themselves as perfect, incorruptible and in control of themselves) it's deeply troubling and offensive.
Really accepting this fact (rather than paying lip-service to it and then continuing to act as if it's not true) is deeply humbling and restrictive. You can't just get angry when you're feeling irritable, because you might not have the right. You can't automatically call others idiots and dismiss their opinions, because you might simply be missing their point. You can't even pride yourself unduly on achievements in the past, because much of what you remember is likely to be (even slightly) self-aggrandising or a distorted account.
This is obviously difficult for many to accept - it feels humbling, and restrictive to personal liberty. However, it probably feels restrictive for a five year-old child to be told not to run out into traffic and to instead learn the Highway Code.
Let there be no doubt; it is restrictive. It's also a part of growing up and taking responsibility for yourself.
There are distinct benefits, however. Aside from helping you become a more reasonable person (always a worthwhile goal), what it does do is give you the opportunity to learn to "step outside" yourself. When you always keep in mind the fact that you might be wrong, it helps you avoid being caught up in events, and allows you to rationally consider not only situations but also your own reactions to those situations in a more calm, considered, objective manner. Instead of merely reacting like a mindless emotional automaton, it allows you to analyse and probe your own emotions, and decide, consciously and rationally whether to pay heed to an emotional impulse or to disregard it as undesirable.
I honestly believe a real, conscious acceptance of one's own fallibility (even in areas we normally automatically assume we're infallible) - and (paradoxically) the opportunity for enhanced self-control that it presents - represents a distinct "level" of cognition (in terms of self-awareness, rationalism, "enlightenment" and the like) that many or even most people simply never advance to. Hell, I know I make a conscious effort to bear this in mind, and I frequently fall far short of the ideal. Nevertheless, I think the goal is a worthy one.
You can think of the two mind-frames as being exemplified by the following scenario:
If you wake up one morning and hear The Voice Of God, where do you go first? The church, or the psychiatric unit of your local hospital? Many (perhaps most) would instinctively believe in the veracity of their subjective experience and would believe God was talking to them personally. That this is an irrational conclusion is pretty easy to demonstrate, given the relative paucity of sanctified religious prophets compared to the enormous (and rising) incidence of schizophrenia and other mental illnesses.
If on the other hand you'd immediately to to your doctor and ask for a psychiatric evaluation, congratulations - that's exactly the kind of skepticism I'm talking about.
Postscript; a name for this type of skepticism (the title of this post) was coined by a helpful redditor, by analogy to Kohlberg's Stages of Moral Development. I would never presume to describe it so grandly myself, but I think the analogy is a good one.