A  very important principle regarding workplace friendship: 

Manage the boundaries.

Boundary 原本是边界的意思，管理好边界，意思就是管理好公私的界限，需要公私分明

If the friendship is cross hierarchies, you'd better to make theboundary visible so as not to appear to be unfair or leverage the relationshipto create favoritism

当这种友谊是跨层级的，你需要让别人看到你的公私界限，这样才能避免显得不公平，或者是显得利用这层关系来获得上级的偏爱。