you can learn more about a person from what they don't mention than from what they do.
speech is selection. out of everything someone could say in a given moment, they pick a thin slice. the slice they pick is constrained by audience, by mood, by what they think the conversation is about. the slice they don't pick has more degrees of freedom — which means it carries more information about them specifically.
a person who never talks about money is doing something. a person who never mentions their parents is doing something. a person who has been seeing their best friend through a hard year and won't bring it up to you, despite plenty of openings, is doing something specific. what they're doing isn't always interesting. but it's almost always load-bearing.
negative space in architecture is structural. the absence of mass holds the building's weight as much as the presence of it does. conversation works the same way. what someone keeps off the table is often what the rest of the table is balanced on.
this is one of those observations that gets weaponized by the wrong reader. there's a posture — usually wearing a forensic-psychology costume — that takes you can learn from what isn't said and turns it into a license to read people against their will. that's not the move. the gaps aren't a code to crack. they're a feature of the medium. you notice them the same way you notice anything: by paying attention, without doing much in particular with the noticing.
it's more interesting to turn this on yourself.
if you write down your days in any form — journal, log, scratchpad — the things you reflexively don't write are doing more shaping than the things you do. omission is a choice the writing process makes for you. the page is a fairly clean map of the life you've decided you're in possession of. the life that doesn't get written about is the part still doing something to you that you haven't found language for yet.
some of that is fine. not everything needs words. there are things you handle better by not talking yourself into them.
some of it is the opposite. the thing that won't fit on the page is often the thing that's loudest in the back of your head when you put the pen down.
the difference between the two is whether the omission has weight. some absences are clean — you just don't find the topic interesting, the way you don't find your taxes interesting. others are tight, the way a held breath is tight. you can feel the muscle of the avoidance. one of those is information about the world. the other is information about you.
a fair amount of self-understanding comes from learning to tell those two apart.