People who loved once would understand that anything so-called everlasting is a fairy tail only. It is unlikely to have in true life, so it is much preciously once it happened.

曾经恋爱过的都明白，童话式的天长地久只属于童话，属于现实，难得，所以可贵，所以童话！

youdao

In front of me there was once such a perfect Health and Safety Manual, but I did not follow it carefully. I regretted deeply only after the accident happened, however, it was too late.

曾经有一部完善的安全手册放在我面前，我没有好好遵守，等事故发生后我才后悔莫及，人世间最痛苦的事莫过于此。

youdao

For example, the stock market crash of 1929 is repeatedly re-expected even though it only happened once; it's just prominent in our thinking.

929年股市崩盘,就被反复提及,尽管这只发生过一次,但是人们对它影响深刻

耶鲁公开课 - 金融市场课程节选

Our aim is to have between two and three stops at every race, so it's clear that four is too many: in fact, it's only happened once before, in Turkey during our first year in the sport.

CNN: Pirelli admit tire testing 'inadequacies'

It had happened only three times in her life, less than once a decade.

NEWYORKER: Shauntrelle

Dial the 800 number, work through a dizzying array of menu choices, choose to speak with a human being and wait on hold listening to music for 20 minutes to two hours (it happened to me once) and you might reach a person who can (in only 70% of my cases) provide definitive, final help.

FORBES: Time Wasters, Time Savers