Ten Cate said: "Of course it was hard because I worked there with a group of very talented and very young players. The only problem with Ajax is you always lose your best players.
"Two days before qualifying for the Champions League, I lost my two best players and the club ended up with a lot of money. It is kind of frustrating. The decision to leave was a big one but Chelsea and I met at the right moment. They needed someone and I wanted to move and everything came together and everybody is happy."
But in the post-Jose Mourinho era, Ten Cate admits the change will not happen instantly.
Ten Cate declared: "At Barcelona the first half-year was not really a success. But the people kept confidence in our work because they were seeing things improving and at the end of the season, we ended second.
"The next two years we won all the prizes to win in Spain and the Champions League which was a great result of course. But you need to be patient. You cannot do it in one year or one-and-a-half years. You have to work on this."