The day to be happy is today, now!
Why should you constantly work on being happy tomorrow if you can be happy now? Today will always have a tomorrow and that tomorrow will become a today with a tomorrow.... that is, if you choose to be happy tomorrow, there will always be a tomorrow in today.
So why don't you choose to be happy today... now? To choose to be happy now is to accept that happiness is not perfect, it is not complete, but it is possible to be felt and to be lived.
How do you choose to be happy?
Not focusing all your energy and attention on the less good events of life, realizing that even in those moments (especially in those moments) you learn and evolve if you are in the predisposition to overcome them, not stagnating in them.
No one here will tell you that life is peaches and cream, that being happy is very easy and that it does not require some work. Yes, your life has been and will be composed of overwhelmingly happy events, happy events, joyful events, amusing events, normal events, routines, strange events, stressful events, sad events and overwhelmingly sad events. That's life! And if there are events that you cannot control at all, such as the death of a loved one or a marriage proposal, there are other events that depend on you, such as, volunteering and receiving gratitude from the people you help or organizing (or not) meetings that nourish and strengthen friendships.
Because if there is a today and a tomorrow, there is also a yesterday.
What is bad today, tomorrow it will be part of yesterday and the further you go, the further back it will be. You must learn to let go of what was, in order to grab other things that are yet to come... so that you can move on, continue to live and to be happy.
It's not about forgetting, it's about moving forward! It is not easy, but it is essential for you to be happy.