The Syco boss agreed that the ratings dips recorded by the two shows, plus the underwhelming debut outings of Red or Black and The X Factor USA had been "a massive wake-up call".
"We all got a bit smug last year, I certainly got a bit too cocky," he told reporters. "I ended 2010 on a real high, it was the Matt Cardle year - my favourite year - and the figures for X Factor were huge.
"I did get too arrogant, everyone does. When you have a very good year like I did in 2010 you get a bit cocky. You think you are great, then you get a bit of a smack.
"We went into 2011 thinking, 'It's all going to be easy', and of course it wasn't. It was a massive wake-up call. From BGT, to Red or Black - me making these massive predictions in America... Last year was the year my ego was put in check."
Cowell said that he was looking forward to starting afresh in 2012 and working hard to make his shows the best they can be.
"It wasn't a terrible year, but 2010 was spectacular," he said. "It feels like I'm back at the beginning again. I am optimistic - but not so arrogant, I'd say."
Cowell has also revealed his intention to have the next Britain's Got Talent winner perform in space.