I am sure some will not relate, but for others it may hit home...I will use myself as an example.
For many trips, I would say the majority of them...Day 1 & 2 are high moral basically no matter what.
Then that 3rd day hits and typically day 3 is my hurdle of the trip. If I can mentally get thru day 3 it is a good forecast for the rest of the trip.
When I am on a 3 day trip, I don't want to end on day 3. On a 9 day trip, day 3 is a hurdle.
Let me paint the picture...
Desk job full time, grinding out the 10 mile road walks and weekend hikes all year but for the majority of time...not conditioning.
I plop myself some wheres along a long trail for a 9 day extravaganza of crushing miles and the timeclock starts. Mental and physical for me.
By morning 3 I am about 50 miles into the walk, physical drain is well underway and depending on how the mental game is that trip determines what my brain starts telling me. Its a fight.
Sometimes the mental game has gotten the better of me and I go home early. I HATE THIS WITH A PASSION. All that planning, expense, and dreaming down the crapper in the matter of a few hours and choices.
Then I get home, and within 24 hours I am kicking my rear for not staying.
So for me personally from lessons learned, from now on outside of a physical injury - I will require myself to stay on trail(or in a hotel) 2 nights before I come home early. What typically happens for me when I have quit is, I will get to a town and stay the night, the next day I get up, feel like crap either mentally or physically and say "I don't wanna do this anymore, I am going home" and then I make up my best excuse to tell friends and family why I didn't meet my goal and I swallow the pride.
Now sometimes I have had a viable reason, like when the foot pads completely disconnected from my feet last year on the CDT....I could have probably gotten another 20 miles or so out of that trip but its whatever....
other times though I have (LOL) blamed it on the trail being too muddy, or being sick/ exhausted, too much rain....blah blah blah goes the crap horn. Its like my brain goes into the same mode as a drug addict goes into with a fix, but my brain is working on an excuse to quit instead of the fix for an addict.
Lastly, I feel like I am a pretty self aware person...And I feel like at 36 my psyche is evolving a bit..not just with hiking but with life ie what is important, what I value, what I approve of and what I dont...but specifically to quitting, I feel like I am quitting less as I get older. Improved mental health? More experience = better plan = less failure? Finally got tired of quitting?
Disclaimer: I am referencing about 5-6 hikes out of 5k miles of walking, but boy do those 5-6 really grind my gears looking back!