As any Boston Celtics fan with a pair of working eyes knows, the Celtics offense can very closely resemble a driver stuck in traffic — moving nowhere fast, it makes less sense to dwell on the lack of forward progress than it does to blast music, telephone a friend and generally do whatever you can to keep your mind off all the goddamn cars stuck in place.

As Paul Flannery writes, the Celtics have been this bad offensively all season. There are several reasons why they finished the regular season with the 24th-most efficient offense. (WEEI)

Their four core players are responsible for more than half their points. Three of them are aging veterans with injury problems — severe injury problems in the cases ofPaul Pierce and Ray Allen – and the other is a point guard who makes about 45 percent of his shots and isn’t a consistent outside shooter.

Without many shot creators, they rely on spacing for their offense and that requires ball movement, pacing and sharp decisions. If any of those three factors break down, it can get ugly real fast. They live and die with their shooting percentage, and with an emphasis on perimeter shooting big men who spread the floor, they are primarily a jump-shooting team with”out much of a low post presence.

Unlike past seasons, the Celtics don’t use the 3-point shot to bail them out. They still shot a high percentage, but they took only 15 per game, one of only seven teams to take less than 1,000 attempts from behind the arc. During the regular season, they took more long-range jumpers than they had attempts at the rim. The area outside the paint and in front of the 3-point line is no-man’s land for most teams, but it’s where the C’s either feast or starve.

The league’s most efficient offenses normally hit plenty of three-pointers and draw free throws at high rates. The Celtics do neither. They can still score explosively at times (think: the final outing against the Miami Heat this season), but it takes executing at a high level on every possession and hitting their mid-range jump shots (normally the least efficient shot in basketball).

As Doc Rivers explained after Game 2, “I don’t think we have a big margin of error.” The Miami Heat can occasionally get away with bad offense because they excel in transition and get to the line more frequently than any other squad. Most of the other elite teams, similar story. The Spurs kill teams with ball movement and drill more trifectas than any other team. But the Celtics need to operate smoothly and rhythmically for an entire contest, or else they will be stuck in goddamn traffic all morning.

The Celtics offense is more laborious than natural. It’s why they’ve played so many ugly games so far, and it’s why they have a considerably smaller margin of error than almost any other team remaining in the playoffs.