What I mean is: some boolean flags are perfect for the real world phenomenon they are representing e.g. is_light_on makes you understand perfectly that when it is true the light is on and when it is false the light is off.
There are other cases in which if you didn’t write the code and you don’t read any additional documentation, everything is not clear just by looking at the variable name e.g. is_person_standing, when true it’s clear what that means but when false, is the person sitting? Lying? Kneeling?
I’m obviously not talking about cases in which there are more states, boolean would of course not be a good solution in those cases. I’m talking about programs in which there are only two states but it’s not obvious, without external knowledge, which ones they are.
Our IT often use a Boolean as a shortcut for figuring out things in code. For example, if there’s a charge we don’t apply to some customers, instead of setting it to zero, they’ll have a Boolean on the customer to decide whether they skip that part of the calculation. On top of this, they then name it in a way that limits how many records they have to update, this leads to many settings phrased in the negative, such as “Don’t apply extra leg charges”. As an extra layer on this, more recently they were made aware of the confusion this causes for staff and their solution was to change how end users are the question, which causes the “yes/no” in the interface to read the opposite of the “true/false” in the database