Start, not finish
https://gyazo.com/93ac73d5aa90f566b13ee4a5f84f5fc0
There is a boundary between qualitatively different things A and B when they are continuous on a time axis.
At the timing of this boundary, A ends and B begins. Therefore, "it is the end and the beginning" is logically correct, but since humans often recognize the familiar A and not so much the unfamiliar B, the sense that "A has ended" becomes stronger.
Related and more specific
You feel like things are complete when you've succeeded in taking the exam and getting into the school of your choice.
The entrance exam has been completed, but a new life at the university is about to begin, so it is more appropriate to have "the feeling of completion" rather than "the feeling of completion". You think "it's over" when the tutorial is over and the main game is about to begin.
---
This page is auto-translated from /nishio/ゴールではなくスタート. If you looks something interesting but the auto-translated English is not good enough to understand it, feel free to let me know at @nishio_en. I'm very happy to spread my thought to non-Japanese readers.