[thebluesky]

Figuring our how core libraries such as the collections framework work is pretty easy if you get a good book like Scala for the Impatient.

[notimetorelax]

It's not only core libraries, all the available libraries that your project depends upon will one day or the other have to be debugged. I mean I had to debug Hibernate and it was a pain, I can't imagine debugging something written with advanced Scala features that I'm not very confident with.