An eternal perspective
Given that you will always have more days ahead than behind, it is absolutely certain (for believers) that your “best” days are yet to come. Those days will be better than these not just because they come later (especially in the light of eternity), but because we must build upon the things we learn today. The biggest thing that separates yesterday from today and today from tomorrow are the people in them: who we can interact with, who we can help, who we can serve, who we can bless, who may be in our far-distant-future because of the Good News we brought them today. The only treasures we bring into the farthest future are the character we have grown, the lessons we have learned, and the people we have built (1 Corinthians 3).