"I saw that online," Williams told the BBC. "I get where he's coming from."
"I find it difficult forming words in my head without an audience. So when there's 16,000 people screaming at you while you're trying to talk, I get it."
But he said Bieber was wrong to scold his fans: "You've got to do it with humour or you don't do it at all."
Bieber's UK tour was marred by ill-tempered rants at the audience. He called fans in Birmingham "obnoxious" and walked off stage in Manchester when screams drowned out his voice as he spoke between songs.
"I don't think it's necessary when I'm trying to say something and you guys are screaming," the 22-year-old told them.
He later reappeared to finish the concert, saying: "I'm not going to talk the rest of the night. We're just going to do the music. Obviously Manchester just can't handle it so let's do the music."
Williams, who said he had seen coverage of the incidents, added: "I was like, this attention deficit disorder's really getting in the way for him. That's what I felt like, without even knowing that he'd got it."
He later discovered that Bieber had talked about his struggles with ADHD, revealing to GQ magazine that he was taking the stimulant Adderall to help him concentrate.
After finding fame with Take That, Williams also suffered anxiety and depression and said he had struggled on tour in the past.
"Sometimes it's work and sometimes there's a communication with my audience that feels otherworldly," he explained.
David's Song, a track on the star's new album, was inspired by one such moment.
"I was actually on stage and I was having the most perfect moment with the audience, and I thought 'If I died right now, life has been absolutely amazing'.
"It can be that good on stage. Then on other nights, it's just me acting like I'm enjoying myself because that's what they've paid for me to do. That's just the rhythm of life".
Williams said that having a family had helped him overcome his anxiety about playing live.
"I'm a daddy, so I have a purpose," he said. "It all makes sense. I'm a working dad, whereas before I was the textbook pop star who wasn't happy, even though he's got all this stuff."
He added that his marriage to Ayda Field had changed the way he behaves on stage.
"I don't think I'm as touch-feely as I used to be with the audience," he said. "I can't do that now I've got a wife.
"I guess that I'm not as sexually-orientated. That's not the same any more. [Family] has made me want to be a better performer, better singer, better songwriter, better lyricist. The sense of responsibility has made me fine-tune my game."
The star also confirmed he would not be reuniting with Take That to mark the band's 25th anniversary in 2017.
"We unfortunately couldn't get our diaries to match. We will be doing something but I don't think it'll be next year."
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Robbie Williams says he sympathises with Justin Bieber, after the Canadian pop star reprimanded audiences for screaming at his concerts.