As Stunted points out , the liklihood of falling , tripping lessens with the the amount of experience and tramping one does.
Personally when i was in the hills a lot walking on tracks as part of my job i cant ever remember having a fall, maybe a stumble or two though where tree roots are a curse(Barra track Pines to Mitre Flats Hut comes to mind).
My own perception is that as you walk looking down at the track the picture of where you are walking is transmitted through the senses to your legs and feet; the more experience/time you spend on your feet this reaction eventually becomes a subconsious reaction and your feet
just go in the right places.Very much like any repetitive task , i imagine.
The major problem of course is that most people are unable to spend vast amounts of time walking around in the bush getting this type of experience.
For some of us who have ,its a skill well worth having , especially as we get older.
