The former Atletico Madrid man faced widespread criticism after a string of poor performances, but has since established himself as one of the Premier League's top goalkeepers.
De Gea is now confident he can challenge Alex Stepney's record of 433 appearances by a United keeper.
"They were difficult times. It was hard for me," he told The Sun.
"It wasn't easy hearing criticism but I tried to use it to motivate me and make stronger.
"I like to think that from bad things you can derive good results."
The Spanish U21 international has admitted that he found it difficult to move away from Madrid and that he felt the weight of expectation following his £17.8m move to the Red Devils.
"I was very young. I had arrived at a new club from another country, I was learning a whole new language, I was adapting to a new style of football and new team-mates," he said.
"That's a lot to take in and I think it's natural that it will take a little bit of time to settle."