Some hikers thrive on a difficult trip while others wear down quickly.
To survive & thrive, most importantly, avoid getting sick.
Be sure that standards of hygiene are maintained. Faecal contamination of any kind is the easiest way to get sick. Be sure to put alcohol-based antibacterial gel on your hands throughout the day, particularly before you stick your hands into a bag of GORP. (Especially on Misti when you have very little water for washing.)
Al Brawn in Soaring with the Eagles cites a statistic from Tilton (Gut Reactions)
Viral syndromes & diarrhoea account for 60% of the illnesses and 45% of the illness evacuations (from wilderness programs)!
Proper food and safe, sufficient water are essential.