Nowadays there are few clubs in the Premier League that would stick with their manager through thick and thin. The days of the board being loyal to their manager were over a long time ago.
If Chelsea sack Pochettino there is not a large pool of available managers to choose from therefore it will almost be like they are taking a step back. After they made a mistake hiring Potter they need stability and for that Pochettino is the best option for Chelsea. They are fortunate to have him and he must be given time to manage the team.
Poch's success is anything but assured. Remember, they also got rid of their greatest manager yet in Mourinho. So that shows that nobody is immune from the inevitable sacking if the team doesn't get the results.
It's just the way football is right now. It's a bad culture and it's really sad to see that almost no club would be willing to stick with their manager through thick and thin.