To run long, you need to train long.
To run fast, you need to train fast.
To endure a trail, you must train on trails.
To endure a multi-day race, you need to train consecutive multiples of day.
Simply put, it’s really just that. What is more complicated is the details on the HOW.
Either you search the net on your own or you get someone to teach you.
Either you do something free, or pay.
Everything is always about the choice we make.
It’s also that simple.