Propensities, or character
There is a crack in all things: that's where the light gets in
There is no such thing as a man for all seasons
350 words, 2010 revised slightly 2025
Part of character is a set of propensities. In the case of a good character, it may involve a propensity (a habit) to err on the side of courage, patience, perseverance, generosity, etc. But a good character might equally err on the side of safety-first, caution, decisiveness and thrift. (There is no exact mirror-image here.).
Part of soundness of character is a degree of constancy. If your behaviour is all over the place in some respect you cannot be said to have the propensity or habit (characteristic) in question.
Character reflects the fact that we do not take most decisions, whether moral or other kinds of decision, on a case-by-case basis. It is not that we follow a rule necessarily, but an observer might be able to discern a pattern. One may take this line of thought further and say that it is not just a matter of fact (a fact about human nature) that we do not take decisions – everyday decisions – on a case-by-case basis. The decisions must be based on the perceptions and motives of a self that has a semblance of unity. If a character is wholly unpredictable, we are likely to consider it defective. (Some such people get locked up if the nature of their unpredictability is such as make them a danger to others.)
Moreover, many decisions need to be taken instantaneously. If your character is unformed, your decisions will be haphazard, or you will make decisions by default, i.e. by failing to act.
At the beginning, I described character as a propensity to err in a particular direction. If this is true of one person's character, the corollary is that some other persons will err in the other.
It might seem unfortunate that people should err, in whatever direction. But it is not only a somewhat obvious fact; it is, surely, a necessary fact given that we are social animals.