All this reminds of something I noticed a while back. Had such an impact, I wrote it down in a journal.

"I've now been on two kinds of tours. The kind where I train for weeks climbing hills and hauling weight, crunching numbers and poring over maps, charting elevation gain and loss, gear inches, and gain ratios. Also the kind where I just hop on my bike and take off with whatever I throw in my panniers that I think I might need for a week or two, no cyclometer, no maps, no watch. Hard to say which is better, and maybe both should be part of the regular rotation."

To this day, I couldn't tell you which kind of touring I enjoyed more. They are both appealing in different ways. I think I definitely do more planning and prepping for tours these days, and that is probably why I am occasionally able to "just go" without thinking about it too much.

Erick L is right on about the mental aspect. Don't stress over your physical conditioning... after a week of mountain passes, off and on rain, and headwinds, how do you feel? Having a good time? Why not? It's all in your head.

I find it helpful to convert bitter complaining and wishing things weren't as they are to something more positive while on tour:
"More wind please!" - my personal mantra for dealing with headwinds that just won't quit.
"Another mountain? I just love mountains!"
"Well, it's been 3 days since I last showered, can it rain a little harder, please?"