Assume a project, in an ideal world where deadlines are never missed or over-estimated, with a 3.5-month hard-deadline, equating to 100 days for the sake of the argument.
The team consists of the very best talent in the industry. Amongst whom are the greatest project managers a product owner could ever possibly ask for.
The delivery team have sat down and planned a detailed daily delivery of this project. Knowing exactly what needs to be delivered on a daily basis, and in what order.
The whole idea is to achieve the 100-day deadline, by achieving 100 mini-deadlines each day.
In order for this project to hit its deadline on the 100th day, it needs to hit its deadline on the 50th day. Then it needs to hit its deadline on the 75th day, then on the 87th day at midday (assuming you work from 8AM to 4PM), then 93th day at 2PM, then some time before COB on the 96th day, and so on and so forth.
Clearly the project will never reach the 100th day as there is always work, no matter how big or small, that needs to be done.
There you have it folks. Completion of any given project is impossible and what we perceive as completion is nothing but an illusion.