I think this is the kind of advice you give to someone at a funeral, when they've been mourning for some time, in order to tell them to not continue morning needlessly. Its not saying you shouldn't mourn at all. Remember, only Sith deal in absolutes.

This philosophy stems from Buddhism which emphasizes a lack of detachment from material possessions and personal connections. Not to mention that if one truly believes that the person they've lost is in a better place now then there's no reason to give undue weight to your own personal loss of access to that person.