England will need Hart at his best in tomorrow night's World Cup qualifier in Ukraine.
"Goalkeepers at that age make mistakes," Martyn told talkSPORT. "We've all done it.
"The pressure nowadays means they're not allowed to make those mistakes. I made mistakes at that age though, as did David Seaman, Peter Shilton and many other great goalkeepers. It's going to happen.
"His temperament is spot on for the job though, he'll go to Ukraine confident that he can produce a good performance."
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