Pietersen who quit ODIs and T20s recently due to ECB's policy, which doesn't allow cricketers to choose any of the limited overs formats, as the policy states the cricketer should be available for both ODIs and T20s or only Tests.
Smith reacting on Pietersen's exit, said it will be very difficult for the South African-born Pietersen to digest that he has quit ODIs and T20s when he was at his prime, as it leaves a big hole in his life.
"It's impossible to know what you're giving up, and how hard it will hit you, until it's gone," Smith, who has had plenty of run-ins with Pietersen in the past, told online magazine Wisden EXTRA on Monday.
"One-day cricket has been a big part of his life for a very long time and, right now, he thinks he can just walk away from it.
"Maybe he can. But I think he'll quickly find there's a big hole in his life which isn't as easy to cope with as he may think.
Pietersen suggested that he could come back and play for England and also hoped if he could serve for his nation during September's ICC World T20 as England defend their title which meant a lot to the batsman as he was the man of the tournament during the previous edition that was played in the Carribean.
Smith also said that he wasn't aware of the happenings siad that if Pietersen's decision to quit ODIs and T20s was based on the disagreements with ECB then his comeback would be impossible as it doesn't seem to come to an end.
"I don't have any inside information at all, so I'm just looking from the outside, but if there's any truth that his decision was partly based on the disagreements he had with the ECB and the way they treated him, then I believe he'll find it even harder to come to terms with the way his one-day career has ended.
Smith further said that, the South Africa-born Pietersen should have played for a few more years as he was at his best especially during the last few years.
"He just seemed to be back to his aggressive, attacking best, too. Very strange that he should give it away."