This is a great idea. It's a twist on writing down your goals, but with a more personal touch.

It reminds me of Daniel Kahneman's eye-opening concept of the "experiencing self" and the "remembering self." He has discovered that these often do not align - which explains how it is possible to be at the verge of a nervous breakdown when looking after young children, for example, and yet tell people you like being a parent (speaking from experience, here!).

By writing to an older version of yourself, it helps you put the hard work into perspective that you are doing and gives you motivation to see it through. It reminds you that it does indeed serve a purpose in the long run.