Too late to upvote! I was just perusing the latest issue of SteemStem Distilled when I came across this.  Wanted to add something even though it's past payout.  The letter writing is wonderful, especially writing one with a date far in the future as a way of being forward thinking.  Putting the past behind is essential, while at the same time acknowledging its influence on the present.  And, finally, finding pleasure in the present is the best way to put the past to rest.  
I think there is one more piece to finding happiness, or at least satisfaction in life, in the present.  Stop focusing on yourself.  Look outward. Reach out and find someone or something you can help.  This gives a sense of control, because you have affected someone's life positively, and it is very rewarding to be helpful.  By reaching out you make the  present a dynamic experience.  I remember a quote from Rabindranath Tagore: ["I acted, and behold service was joy."](https://www.brainyquote.com/quotes/rabindranath_tagore_134933) .  There is more to the quote--it's worth following the link.
Anyway, I wouldn't be the first, and certainly not the wisest, person to suggest that being useful brings satisfaction.  Don't have to be useful in a big dramatic way...little things that make a difference to someone or something, will actually make a positive difference in your own life.
Good post.  Hope you don't mind the late response.