Which parts of 5-1 Vikings' success are sustainable (and which aren't)?

A clutch fourth-quarter touchdown drive. A key field goal made, then an opponent field goal hitting both the upright and crossbar before falling short. Another clutch drive and timely turnover. Getting outgained by a 2-to-1 margin but still coming out on top.

The Vikings can't keep winning like this, we keep saying week after week, as they keep winning like this.

The only concrete reality that matters in the moment is that the Vikings are 5-1 at the bye, with a two-game lead in the NFC North, over teams that seem perhaps even worse than advertised when the season began.

But where this is all going is a relevant question that often comes down to whether you think the manner in which the Vikings are winning is sustainable over 17 games.

Within that question is a great deal of nuance. Here's how I see the discussion best framed, much of which we talked about on the latest Access Vikings podcast.

Sustainable: End of game confidence. When a team wins a lot of close games, there is a cumulative confidence that builds. Vikings writer Ben Goessling often points to the 2012 Vikings, who unexpectedly started 4-1 and used that confidence to finish 10-6. Believing you are going to win is a surprisingly large part of the battle, and the Vikings are a team that believes in themselves when games are on the line.

Not sustainable: End of game outcomes. That said, there is a point where confidence meets the law of averages. Football Outsiders has the Vikings at No. 17 in overall DVOA (strength) and says their performance so far should have yielded 2.8 wins. If we round up. let's say 3-3 is fair — two close wins and two closes losses in the last four. Being 5-1 is all that matters, and confidence might lead to more wins than losses in tight games, but eventually a bounce will go against them. Speaking of which ...

Sustainable: Turnover differential. The Vikings are tied for No. 2 in the NFL with a plus-4 turnover differential, a stat that overwhelmingly correlates to success (Philadelphia, the only undefeated team, is No. 1 at a whopping plus-12). The Vikings emphasize takeaways (10 so far), and they are believers in "you get what you emphasize." They can continue to be a plus team in that category.

Not sustainable: Turnover timing. What doesn't feel as sustainable, at least, is when those takeaways happen. In particular, game-changing fumble recoveries against the Bears and Dolphins in the fourth quarter are plays that won't always be made when it matters most.

Sustainable: Bend-but-don't-break-philosophy. The Vikings are giving up 6 yards per play and 7.3 yards per pass attempt, both of which are in the bottom five of the NFL. But because of the aforementioned turnovers and some red zone success, they're tied for No. 11 in points allowed per game at a shade under 20. Kevin O'Connell often says "make them snap it one more time," so this is no accident. They will live with yards allowed.

Not sustainable: Bend-but-don't-break results. Still, against more efficient offenses that don't hurt themselves with turnovers and penalties, a team that bends often will eventually break. The yards allowed need to come down for success to be sustainable.

Sustainable: Continuing to imagine this team will get better. The biggest thing the Vikings have going for them, aside from their record, is the idea that they will continue to improve as they become more familiar with their offensive and defensive systems. Improvement should be sustainable, particularly with a well-timed bye week that will allow coaches and players to evaluate what is working and what isn't.

Not sustainable: Continuing to win at this rate if it doesn't. If the Vikings don't markedly improve? They might still win the division because of the cushion they've built and the belief they have, but they will eventually lose to a better team. And their post-bye results will probably skew closer to .500 than .800.