The Portuguese tactician was appointed at Stamford Bridge in the summer of 2011 as the most highly-rated young coach in Europe, but lasted just nine months.
"Not everything we did there was wrong, but we could have done better. It has not affected the way I am viewing football, but I admit I thought a lot about it.
"I should have been given an opportunity to go on, but I am aware that, considering the results, change is the only way to make an impact.
"I would never have gone to Chelsea if I was not absolutely convinced that I could have been a success there."