Every year, 12 out of 32 teams make the NFL playoffs, which means that prior to Week 1, each NFL team had a 12 out of 32 chance (37.5%) of making the playoffs.
But those odds went out the window with the season openers. Because of the brevity of the NFL season with just 16 games, every game carries an inordinate weight in determining a team's playoff odds. After Week 1, the playoff odds will have shifted significantly from the 37.5% all teams shared before kickoff weekend.
In the 15 seasons since realignment, from 2002-2016, 240 teams won their season opener. 121 of those teams (50%) also made the playoffs. Conversely, only 25% of the teams that lost their season opener (59/240) eventually made the playoffs over the same period, as the table below illustrates.
If you're one of the teams that stumbled out of the gates on opening weekend, your 0-1 record means next week's game is already something of a must-win game. Start the season 0-2 and your odds of making the playoffs drop to just 9%. Lose the game after that and you can start looking at mock drafts for 2018; no team in the last 15 years has made the playoffs after losing its first three games.
The Cowboys got a win yesterday, and that puts them in the green in the table above. But the brevity of the NFL season also means that if they don't follow up that initial win with more wins, they could be out of the playoff race pretty fast.
For now though, the Cowboys have done what needed to be done and started their season “in the green.” And if they continue winning, there's no reason why they shouldn't stay there until they have a playoff spot locked up.