Ask HN: What is something you achieved that you once thought was impossible?
For me it was SF half marathon. I had a broken knee year before that, I was able to do thisthanks to meditation, great coach and encouraging group of people.
If you've always wanted to do it, I would recommend doing longer and longer hikes and then just do the big one.
In my case I started with 2-3 day hikes, expanded to 10 day hikes and then just did the 10 month. A 10 month hike is essentially a series of 10 day hikes, because even in a 10 month hike after 10 days of hiking one just takes it easy or rests.