just one of those things

just one of those things

An unexpected or random occurrence. This phrase is often used when one wants to dismiss something without further discussion or concern. A: "I thought you weren't coming!" B: "Oh, you know, my schedule cleared up at the last minute—it was just one of those things." Getting sick is just one of those things, Mom. Don't worry about it!
See also: just, of, one, thing, those
Farlex Dictionary of Idioms.

just one of those things

A random occurrence that can't be explained. For example, It wasn't their fault that the show failed; it was just one of those things. This expression was given greater currency as the title and refrain of one of Cole Porter's most popular songs ("Just One of Those Things," 1935). [c. 1930] Also see one of those days.
See also: just, of, one, thing, those
The American Heritage® Dictionary of Idioms by Christine Ammer.

just one of those things

If you say that something is just one of those things, you mean that it is something that happens and you cannot explain it or prevent it. `I wonder why.' Mr. Dambar shrugged. `It must be just one of those things, I guess.' It was no-one's fault — just one of those things.
See also: just, of, one, thing, those
Collins COBUILD Idioms Dictionary, 3rd ed.
See also:
  • better late than never
  • for the best
  • all for the best
  • human interest
  • bonus
  • Bonus!
  • if I had (some monetary unit) for every (something)
  • chain reaction
  • a one-off
  • stroke of fortune