The long season erodes a thin squad predictably
A team's best eleven players, judged on paper at the start of a season, rarely all remain fit and available at once for very long once fixtures accumulate. Injuries, suspensions and fatigue are not random shocks so much as predictable consequences of playing dozens of matches across many months, and a squad's true quality is best measured not by its strongest possible eleven but by how little it drops off when forced to field its twelfth, fifteenth or eighteenth most important player during a busy stretch of the calendar.
Where the gap actually shows up
The matches that decide a long season are rarely the marquee fixtures against the strongest opposition, where every squad tends to field its best available players regardless of depth. They are the unremarkable midweek fixtures against modest opposition played with a weakened team, and it is precisely there that the difference between a deep squad and a thin one becomes visible in the table. A club with a significant gap between its starters and replacements tends to drop points in exactly these low-profile matches, which accumulate quietly across a season far more than any single high-profile defeat.
Depth as a strategic asset, not just insurance
Squad depth is not purely defensive insurance against bad luck; it is also a strategic asset that allows a manager to rotate deliberately across competitions, resting key players for less important fixtures without materially weakening the team fielded. This flexibility compounds over a season, reducing fatigue-related decline in a team's best players precisely when it matters most, in the closing weeks when quality but tired squads elsewhere in the competition begin to show the physical cost of having had no comparable depth to call upon.