After U2 played Glastonbury in 2011, they were criticised by the crowd and media for not putting on the most tip-top performance. In response to this, lead singer Bono claimed that the reason they didn’t move about the stage, was as much due to the fact that the floor was like an "ice rink" and that he wasn’t wearing very good shoes.
If he didn’t have suitable grip on the floor, then Bono could have fallen off the stage, which could have been even worse than the decidedly static performance. (Or perhaps better if you’re not a fan of the band!)
However, I think the real reason for the disappointing performance, is that there had been an unreported internal tiff between Bono and the lead guitarist. I suspect that this was over the fact the Irish frontman hadn’t worn the new footwear his buddy had given him as present the day before.
And although he explained this to the media, it was obviously misunderstood and turned into the slippery stage story.
If you go back and research it, I wouldn't be surprised to discover that the exact quote from Bono would have been something like “I was wearing the wrong shoes and I didn’t want to get too close to The Edge."
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