Yes, you are probably right. But do you think there is a danger that if you know your characters too well they become less flexible in their actions? For example, if a character is nervous then their nerves have to be always taken into account. Whereas if you have a character who has simply done A, B and C then one has more flexibility to decide how they might act when it comes to D (if that makes any sense...).
We may be arguing in violent agreement here.
How do you get to know a real person? You observe them, listen to them, talk to them and observe their response, watch how they interact with other people. You create a three-dimensional image in your head of how that person thinks until soon, you can usually predict their actions.
Early in the story, when I know little about them, every new action has to be seen in light of how it fits in with their character so far. The character builds and takes on more definition. Their actions become constrained because you have a clearer picture of how they would react when new situations come along.
For example, if a character is dishonest in small ways at the beginning, it's more likely s/he'd go along with a truly evil scheme later. But if they're scrupulously honest, then getting them to participate in a great crime would require the greatest of threats and inducements.
Add to that the fact that real people occasionally do things completely out of whack with our vision of them. EG, the apparently contented housewife has an affair or runs away. This disconnect, when it happens in real life, is often profoundly disturbing to us.
But because we're writing fiction, it has to make sense, so there has to be a cause somewhere in their history. So you add that to what you know about them, too.
Basically, this is the same process you use when you get to know real people. You build up layers of knowledge about them until you can predict, or at least explain, how they'll react in new situations.
Building characters in this way works, but there are consequences:
1. Characterization is poor in the early chapters and they generally have to be rewritten in view of how the characters develop later.
2. When I work with an outline, I generally have to abandon it after a few chapters, because the original conception of the plot is no longer consistent with the growing characters.