Because you confuse the enthusiasm of beginning with the motivation to finish. They are two completely different energies. The beginning is exciting because it is full of possibilities; the middle of the journey is boring because it is full of repetition. The pattern of quitting always activates at the same point: when the novelty fades and only the work remains. The secret is not finding the right thing to start — it is learning to stay when the excitement is over.
What the letters say
From Letter 01 — Here we go again
The next day I was in front of a screen unaware of what I was looking at, but aware that something was starting to move.
From Letter 02 — Choosing who to be
And that's where I understood the first mistake. I wasn't competing with them. I was competing with my idea of them. So I was already defeated before I started.
Every morning I started doing something simple. I get up, and before doing anything else, I ask myself: who do I choose to be today?
From Letter 03 — The price no one wants to pay
Until difficulty stops scaring you and starts exciting you. Because you understand that on the other side there's always something worth more than what you're leaving behind.