Let me give you a 'fer instance' (this may be the only one that exists, but it's one that had me WTFing until I found the correct documentation to read via stack overflow)

Calling grouped on a Seq.

I've been playing around with some API requests, and needed to batch a long Seq to make reasonable sized GET requests.

So I called grouped on a Seq, then to sanity check I called .length on the grouping.

Then suddenly I had an empty iterator.

Maybe I should have known better, yeah, but the documentation I was reading http://www.scala-lang.org/docu/files/collections-api/collect... doesn't mention this fact about iterators. Again, maybe I'm the only person in the world who didn't realise the problem with calling .length on what I thought of as a regular old batched set.

It wasn't until I hit on the right google combination that I found http://www.scala-lang.org/api/current/#scala.collection.Iter... from a stack overflow reference, and the lightbulb finally went on.