It is entirely possible for an NFL quarterback to be successful without displaying pinpoint accuracy with his passing as long as the quarterback makes enough big passing plays. Without the big passing plays, however, there is simply no chance for a quarterback to be even average in his level of production.
The problem with Mornhinweg's assessment of the importance of a quarterback's completion percentage is that it does not necessarily apply to Mark Sanchez, who is the presumptive favorite to be the starting quarterback for the Jets next season.
For Sanchez, his completion percentage in games has a strong correlation with the most important statistics for a quarterback. So in fact, Sanchez's completion percentage on a game by game basis is very much linked with the success he has had.
Using Mark Sanchez's game logs, provided by NFL.com, I took each of the 67 games in which he has been the primary quarterback for the Jets and ran a correlation between his games' completion percentage and his yards per pass attempt, adjusted yards per pass attempt, net yards per pass attempt, adjusted net yards per pass attempt, yards per completion, touchdown percentage, interception percentage, sack percentage, fumbles lost percentage and his QBR, a statistic provided by ESPN.com.
First, the good news.
Mornhinweg and all Jets faithful will be glad to know that no matter what Sanchez's completion percentage is in a game, it has little to no relationship with his yards per completion, touchdown percentage, interception percentage, sack percentage, and fumbles lost percentage.
Unfortunately, the problem is that even without his completion percentage mattering in those statistical categories, Sanchez has still been decidedly below average in them for his four-year career.
The good news that was actually not good news at all gets even worse when you look at the correlation between Sanchez's completion percentage and some of the most important statistics for a quarterback: yards per pass attempt (0.641), adjusted yards per pass attempt (0.625), net yards per pass attempt (0.619), adjusted net yards per pass attempt (0.615) and QBR (0.634).
Each of those positive correlations is strong, meaning that Sanchez's completion percentage in games is very much related to how the rest of his statistics look.
Even in his rookie season, when Sanchez had his highest yards per completion average and making his biggest pass plays, his completion percentage still had a strong correlation to his yards per pass attempt (0.694), adjusted yards per pass attempt (.707), net yards per pass attempt (0.636), adjusted net yards per pass attempt (0.694) and QBR (0.678).
Other quarterbacks might be able to succeed without great completion percentages, but his career numbers suggest that Sanchez is not one of them. When he has had the most success, it has usually been when his completion percentage is at its highest.