Netziv points out that there is actually a hint to a more difficult message. For just as one should not think that what appears bad is not actually good, so should one not think that what appears good is necessarily not bad: Had the Jews gone straight into the land and not fought with Og and Sichon, all the tribes would have found their rightful place together on the western side of the Jordan. That they didn’t led to their early exile, caused by this very land – which did not fully share in the elevated spiritual properties of the Land of Israel proper – that became their home.
In this regard Moshe’s consolation is a double-edged sword. If the message is “do not be overly upset about what you see as a tragedy,” it also teaches not to get carried away with what you see as reason for celebration. To read more, go to the Jewish Press.