How to counter Sett
Let us take a look on how to beat Sett. We will look at champions who are strong against Sett and who are weak against Sett. Use win rate, gold difference and creep score difference at minute 10 to find the best 
Top champion who counters Sett. You can already win in champion select with the right counters for Sett. If you want to know how to counter Sett then you need to take into account the best picks vs Sett and the worst picks vs Sett. This Sett counter data is based on matches played by Pros on patch 15.1 and previous ones. It is important to see whether Pros counter picked Sett or whether they played as Sett.
Champions used by Pros to counter pick Sett
Looking at the matches from Pros (see table Pros counter picked Sett) we can see that they picked 
Ambessa most often to counter pick Sett. The matchup Ambessa vs Sett occured 14 times. Sett has 10 wins and 4 losses in this matchup. Learn how to counter pick Ambessa to get another perspective on the data.
Lane outcome for Sett
When looking at Sett counters you will notice that win rates alone are not conclusional. Therefore we provide an overview (see table Lane Outcome) where you can see the lane outcome of Pros who played Sett. The lane outcome of Sett consists of three outcomes: Win, Loss or Draw. Let's take a look of Sett lane and match outcome for specific matchups. Considering the lane outcome and the match outcome of a specific matchup, might enable you to find the right counter for Sett.
Conclusion
Analyze the available data and learn how to beat Sett. To master Sett take also a look on Sett builds and runes for Sett. Good luck, Summoner!