Every place where it states: "It was in the days of" [the expression] is one of anguish (Vayikra Rabbah 11:7).
If someone is preoccupied only with nostalgia, dreaming about how idyllic the past was and seeing nothing good about the present, it is a sign of anguish. If someone looks toward the future, planning for and anticipating what can be, it indicates joy.
All our joyous festivals are tied to the future. Although we commemorate the historic Exodus from Egypt on Passover, the second half of the Seder relates to the ultimate Redemption, and we close the Seder with the declaration, "Next year in Jerusalem." While Shavuos does commemorate the revelation at Sinai, it is the commitment to observe the Torah given at Sinai in the future that gives the festival its importance. And the festival of Succos, which culminates in the completion of the annual cycle of reading the Torah, is also the beginning of a new cycle. We always rejoice with the future, not the past.
The past is sure, the future is uncertain. Whatever challenges the past had are behind us, while those of the future must yet be confronted. Yet the uncertain and challenging future should generate joy, because it holds the promise and potential of what might be.
If the past has been one of achievement, it is easy to bask in its glory. However, while comfort might feel better than challenge, challenge is constructive, and joy in life should be sought in what can be done, rather than in what has been done.