The former Reds and Southampton striker announced his retirement this week.
Lambert admits he should have never settled as a bit-part player under Brendan Rodgers.
"I was getting well paid but I never started playing football for the money," he told the Daily Mail.
“And when I decided to go to Liverpool I sacrificed a regular first-team place and that was when I started to fall out of love with it.
“I never should have accepted being on the bench, even though Brendan Rodgers had made it clear to me I would be back-up for Suarez and Sturridge.
“I was never as quick or as technically good as the best players, but in my own head, when it came to actually playing, I could convince myself I was the best.
“But when I joined up with England I felt lucky to be there, and it was the same at Liverpool.
“And when I look back now I realise I lost something mentally as a player, by allowing that to happen."