Software is modest if it does what it can to get out of a person’s way.
The most common actions should be the most easily accessible—a person shouldn’t have to dig around to find something they often use.
In some cases this will mean that a person should be able to customise software so that it suits their most common actions.
Where possible, unnecessary steps and long task flows should be cut.
Software should speed up a person’s ability to make decisions. That includes a lack of distractions while they’re trying to get something done.
It’s important that software doesn’t interrupt people unless it’s absolutely necessary.
All of these things can help contribute to a flow state for the person.