The focus is on lengthening the time that the players can concentrate and the resistance they can work against.
“Small sided games, while no guarantee, are the best way to get children interested in soccer…”
“Over and over again during matches and training sessions, situations occur that are suitable for 'mental training.' This is because these situations have emotional ballast and it concerns a hobby they enjoy. That and playing in a team make it possible for coaches to tactfully mould talented (and not-so-talented) players.” -- Rinus Michels
Small sided games provide an excellent tool for this “mental training.” In fact this is the biggest element that separates them from football drills and exercises.