On The Big Bang Theory Season 8 Episode 13, Sheldon struggles with his new research on dark matter.
Naturally, he's worried that he made a mistake in switching fields of research. I'm glad this is something we are continuing see for Sheldon, since the changes in his career are actually very dramatic.
That would cause emotional turmoil for anyone, so it's good we get a reminder of what has happened. We even see him sulk a little, but that doesn't last.