Last I recalled, it is Yoda's quote:
Train yourself to let go of everything you fear to lose.
It has been mentioned lots of times in the canon that attachment is forbidden for a Jedi. While newbies were little bit "flexible" in this regard, how could Yoda, the grandmaster and the most powerful Jedi, not adhere to this? Why did Yoda save Anakin and Obi-Wan on Geonosis?