Formal mindfulness practice occupies a defined block of time. Informal practice occupies moments already in the day, and in most structured programmes it is not optional.
Formal practice alone tends not to transfer
Sitting quietly is a controlled environment: few demands, a stable posture, nothing requiring a response.
Ordinary life supplies none of those conditions, and a skill practised only under favourable conditions does not reliably appear under unfavourable ones.
Informal practice exists to close that gap by rehearsing the same attention during activities where the conditions are realistic.
The activities chosen are usually automatic ones
Walking, washing up, showering, waiting and eating are the standard candidates, because each is well learned enough to proceed without supervision.
Those are precisely the activities during which the mind wanders most, which makes them the natural place to practise noticing.
They also require no additional time, which removes the main obstacle to daily practice for people whose schedules are already full.
Transitions work particularly well
Moments between activities are natural markers: arriving somewhere, ending a call, closing a laptop, standing up from a desk.
These are already boundaries in the day, so attaching a brief attentional check to them requires no new cue to be constructed.
Transitions are also where the state carried from one activity into the next is set, which makes them the point where a short pause changes the most.
Brevity is the design rather than a compromise
Informal practice is typically measured in breaths rather than minutes, and lengthening it usually causes it to stop happening at all.
The value comes from frequency across a day rather than duration on any occasion, since what is being trained is the act of noticing rather than a sustained state.
Several brief instances distributed through a day therefore do more than one longer episode, which is the opposite of how formal practice is usually approached.
It fails in a predictable way
The common failure is not doing it badly but forgetting it entirely for days at a time, since nothing in the environment prompts it.
Programmes address this by tying practice to a specific recurring event rather than to an intention to be more present generally.
A single reliably cued moment tends to survive far longer than a broad resolution, for the same reason any habit anchored to an existing routine outlasts one that is not.