The Stoic distinction between what is up to us and what is not is widely quoted and usually softened. The original version draws the line in an unusually severe place.
The category of what is up to us is very small
In the surviving handbooks, only judgement, impulse, desire and aversion fall inside our control. Everything else, including the body, reputation and position, falls outside.
That excludes far more than modern paraphrases suggest. Health, the outcome of work, the behaviour of others and even whether an action succeeds are all placed beyond the boundary.
The severity is deliberate. A wide category would leave a person's peace of mind hostage to things that can be taken away.
Externals are ranked but not valued
Stoic writers did not claim that health and wealth are irrelevant. They classed them as preferred, meaning a rational person selects them when possible.
The distinction is between preference and good. One may reasonably pursue health while holding that failing to obtain it does not damage the only thing that matters.
This is where the school separates itself from simple indifference. Action in the world remains fully expected; the attachment to results does not.
Assent is where the work happens
Impressions arrive unbidden, including the first physical shock of fear or anger. What is up to us is whether we agree with the judgement the impression proposes.
An event is described as first appearing, then being interpreted, then being accepted. The interpretive step is where distress is understood to originate.
Practice therefore targets that step, examining impressions before endorsing them rather than attempting to suppress reactions after they have taken hold.
Role obligations remain binding
Withdrawal is not the conclusion. Stoic writers treated social roles as sources of duty, and discharging those duties well is part of living rationally.
A person is expected to act as citizen, parent, neighbour and colleague, with full effort, while holding the outcome loosely.
The often-quoted image is of an archer who aims carefully but recognises that once the arrow leaves, the result is no longer within their control.
Modern uses tend to widen the boundary
Contemporary applications frequently expand what counts as controllable to include effort, habits and choices, which makes the doctrine more actionable and less demanding.
That adaptation is defensible but it changes the argument, since the original force comes precisely from how little is admitted.
Reading the surviving texts directly tends to produce a harder and less comfortable philosophy than the summaries that circulate from it.