There is a moment in every project where the thing goes live and everybody exhales. It is the right moment to celebrate and the wrong moment to stop paying attention, because the ground under a live product keeps moving even when nobody touches the code.
Operating systems update twice a year and withdraw things they used to permit. Browsers change defaults. A payment provider rotates an endpoint. A certificate expires. A phone ships with a screen shape nobody designed for. None of these is anyone's fault, and all of them arrive on a schedule somebody else sets.
The business moves too. The team finds the three screens they use forty times a day and the two features nobody has ever opened. Volume grows past what the first design assumed. A new branch works slightly differently. A product that cannot absorb any of that is finished in the narrow sense and dying in the useful one.
So a handover includes the unglamorous apparatus: training for the whole team, a warranty period, a named person to call, monitoring that tells us before your customer does, and backups we restore on a schedule. After that, maintenance is an arrangement rather than a favour - a regular rhythm of updates, fixes and small improvements.
The alternative is the pattern we keep being called in to rescue. A system that worked on launch day, was never touched, and two years on cannot be updated without being rewritten. That rewrite costs several times what the upkeep would have.