I've seen people commenting that Robert Plant is holding back tears from that performance, but it's not true. He suffers from eye strain due to age. It's gotten more prominent since 2012. And if you look at any YouTube video of him over the past 3 years or so where he's done up close interviews, you will see the same glossy eyed look where it looks as though he's got tears welling up. Just age setting in. He's seen and done it all, many times over. They all have. If anything, sitting through that performance probably bored the hell out of all of them.