I've published quite a lot on people's poor self-knowledge of their own stream of experience (e.g. this and this), and also a bit on our often poor self-knowledge of our attitudes, traits, and moral character. I've increasingly become convinced that an important but relatively neglected source of self-knowledge derives from one's assessment of the outside world -- especially one's assessment of other people.
I am unaware of empirical evidence of the effectiveness of the sort of thing I have in mind (I welcome suggestions!), but here's the intuitive case.
When I'm feeling grumpy, for example, that grumpiness is almost invisible to me. In fact, to say that grumpiness is a feeling doesn't quite get things right: There's isn't, I suspect, a way that it feels from the inside to be in a grumpy mood. Grumpiness, rather, is a disposition to respond to the world in a certain way; and one can have that disposition while one feels, inside, rather neutral or even happy.
When I come home from work, stepping through the front door, I usually feel (I think) neutral to positive. Then I see my wife Pauline and daughter Kate -- and how I evaluate them reveals whether in fact I came through that door grumpy. Suppose the first thing out of Pauline's mouth when I come through the door is, "Hi, Honey! Where did you leave the keys for the van?" I could see this as an annoying way of being greeted, I could take it neutrally in stride, or I could appreciate how Pauline is still juggling chores even as I come home ready to relax. As I strode through that door, I was already disposed to react one way or another to stimuli that might or might not be interpreted as annoying; but that mood-constituting disposition didn't reveal itself until I actually encountered my family. Casual introspection of my feelings as I approached the front door might not have revealed this disposition to me in any reliable way.
Even after I react grumpily or not, I tend to lack self-knowledge. If I react with annoyance to a small request, my first instinct is to turn the blame outward: It is the request that is annoying. That's just a fact about the world! I either ignore my mood or blame Pauline for it. My annoyed reaction seems to me, in the moment, to be the appropriate response to the objective annoyingness of the situation.
Another example: Generally, on my ten-minute drive into work, I listen to classic rock or alternative rock. Some mornings, every song seems trite and bad, and I cycle through the stations disappointed that there's nothing good to listen to. Other mornings, I'm like "Whoa, this Billy Idol song is such a classic!" Only slowly have I learned that this probably says more about my mood than about the real quality of the songs that are either pleasing or displeasing me. Introspectively, before I turn on the radio and notice this pattern of reactions, there's not much there that I can discover that otherwise clues me into my mood. Maybe I could introspect better and find that mood in there somewhere, but over the years I've become convinced that my song assessment is a better mood thermometer, now that I've learned to think of it that way.
One more example: Elsewhere, I've suggested that probably the best way to discover whether one is a jerk is not by introspective reflection ("hm, how much of a jerk am I?") but rather by noticing whether one regularly sees the world through "jerk goggles". Everywhere you turn, are you surrounded by fools and losers, faceless schmoes, boring nonentities? Are you the only reasonable, competent, and interesting person to be found? If so....
As I was drafting this post yesterday, Pauline interrupted me to ask if I wanted to RSVP to a Christmas music singalong in a few weeks. Ugh! How utterly annoying I felt that interruption to be! And then my daughter's phone, plugged into the computer there, wouldn't stop buzzing with text messages. Grrr. Before those interruptions, I would probably have judged that I was in a middling-to-good mood, enjoying being in the flow of drafting out this post. Of course, as those interruptions happened, I thought of how suitable they were to the topic of this post (and indeed I drafted out this very paragraph in response). Now, a day later, my mood is better, and the whole thing strikes me as such a lovely coincidence!
If I sit too long at my desk at work, my energy level falls. Every couple of hours, I try to get up and stroll around campus a bit. Doing so, I can judge my mood by noticing others' faces. If everyone looks beautiful to me, but in a kind of distant, unapproachable way, I am feeling depressed or blue. Every wart or seeming flaw manifests a beautiful uniqueness that I will never know. (Does this match others' phenomenology of depression? Before having noticed this pattern in my reactions to people, I might not have thought this would be how depression feels.) If I am grumpy, others are annoying obstacles. If I am soaring high, others all look like potential friends.
My mood will change as I walk, my energy rising. By the time I loop back around to the Humanities and Social Sciences building, the crowds of students look different than they did when I first stepped out of my office. It seems like they have changed, but of course I'm the one who has changed.