A film's final scene is often shot in the first week and its opening near the end. Shooting order is decided by what is expensive to repeat, and story order is not on that list.
Moving a crew is the dominant cost
A production unit is a large group of people with trucks, lighting, catering and permits attached. Relocating it consumes at least half a day and often more.
If a script visits the same house in scenes four, nineteen and fifty-one, filming those in order means paying to travel there three times.
Grouping them means one trip, one lighting setup for the space, and one permit window. That grouping is what a shooting schedule is.
Actor availability sets hard boundaries
Performers are contracted for a defined number of days, and a well-known actor may have only a short window inside a longer shoot.
Every scene involving that person is compressed into their window regardless of where those scenes fall in the story.
The same applies to children, whose working hours are limited by law, and to animals, who work in short sessions with handlers present.
Locations are available when they are available
A working airport, a courthouse or a stretch of highway is borrowed rather than owned. The owner grants specific hours, often at night or on a single weekend.
Weather forces the same logic. Exterior scenes are scheduled with alternatives ready, so a rained-out day is swapped for an interior sequence rather than lost.
Seasonal appearance matters too, since a park in leaf and the same park bare cannot be intercut without notice.
Continuity is a job rather than an obstacle
The reason the disorder works is that a department exists to track it. Costume state, injuries, hair length, prop positions and the contents of a glass are all logged and photographed.
Emotional continuity is managed by the director and the actors, who need to know precisely where a character sits in their arc on any given morning.
This is the part performers describe as the hardest, since a breakdown scene may be shot before the events that cause it.
What still gets shot in sequence
Some material resists reordering. Physical transformation, where an actor gains or loses weight across a story, sometimes forces a chronological block.
Long improvised sequences and films built around a child's visible growth do the same. These are treated as exceptions bought at real expense, which is why they are rare enough to be mentioned in interviews.