"Shit happens!" (Shit happens - Wikipedia, the free encyclopedia)
I think Americans really like that expression.
I've learned it on the nice movie "Forrest Gump" - they "explain" there that Forrest Gump himself invented such sentence, while he was running, running and running - hahaha. Did you see that movie? I do recommend.
Well, by the way, back to your post, I would like to add that a good way to learn the expressions you are looking for is by watching American movies with English subtitles over and over again.
P.S.: Dear reader, feel free to correct any mistakes on this post,
Student or Learner