To answer your question, instead I will quote what Abraham Klein (probably the second best referee ever had to say about it)
Throughout his career, Klein was not prepared to fail. The level of his preparation, both physical and mental, was extraordinary. He was not years ahead of his time; he was a generation ahead. "It's a good advantage – not just in refereeing but in everything in life – if you know the person who is standing before you," he says. He would study hours of videos to see what tactics the teams used, which players dived, which tried to bully opponents or referees. In 1970 he arrived early and spent a fortnight in the Camino Royale in Guadalajara, acclimatising and studying teams.
"I know the tactics of the Brazilian players," he says. "I saw that inside the area – or just outside, because of Rivelino's free kicks – that if it was shoulder to shoulder they would be very close to the grass. If you remember the [England] game, [Alan] Mullery with Pele inside the area, shoulder to shoulder and Pele was down. So I tried to learn everything, and also the behaviour when you make your decisions.
