CWBorne said:
The larger aspects of the PT are more often than not, simply not ever mentioned in the OT.
-Warning of excess attachment to people
Yoda does tell Luke he needs to be able to sacrifice his friends for the greater good, and a refusal to do so leads to bad stuff.
Luke almost goes to the Dark side when Vader plays on his feelings for his sister, those feelings themselves, not Luke, the feelings are what betrayed her.