I’m another person that believes some horses are just more or less sensible than the average equine. If it’s nature or nurture I’m not sure.
Just like any other discipline, there are certain attributes one looks for in a trail riding prospect. Average to better than average good sense is one of them.
On the upside! It’s my opinion that the best thing one can do for the less sensible types is turn them out 24/7. My homebred gelding is not terribly sensible. That escalated into a real problem at some point during the three years he was boarded (and being stalled 16 hours a day). It took about a year back at home for him to regain his baseline of less sensible (as opposed to having a melt down and endangering everyone bc he saw a dog’s tail wagging behind a mounting block 100 feet away).
My pony is a smart and sensible critter. He’s “bad”sometimes but he’s thinking not panicking. When my homebred spooks (always at the dumbest things it seems) and proceeds to run around snorting like a fool, the pony yeets around like woohoo I’m faster than you fat boi. Anyone with eyes in their head can see the homebred is scared and the pony is having fun. The pony escaped his bamboo prison and walked himself to my house three times cool as a cucumber. My homebred had a meltdown the time he escaped his paddock and was loose in the adjacent yard for two minutes and took three days to settle down afterwards.
The pony would likely be a trustworthy trail horse post apocalyptic event. The homebred needs to be managed to hack inside the perimeter fence on a calm still day while the neighbors are all at church.