"I've had three interactions so far with fellow passengers. One of them handed me a lovely note - kind words about my documentary - and then asked for a photo," Williams said.
He said he wrote a note back explaining how he'd had little sleep, wrangled four children through the airport, and that his anxiety would spike if they came and took a photo because the whole cabin would then begin wondering who he was.
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A steward then asked for a selfie on behalf of another passenger, before a third passenger then just walked up and asked outright for a selfie, to which he agreed, Williams said.
"There's a kind of unspoken law: as a celebrity, you should be accessible 24/7. Greet all strangers like you're the mayor of the best town anyone's ever visited. Make sure their wishes are met, whatever they are," the singer added.
"Otherwise you're a ****." There's no in-between. I've seen the argument: These people put you where you are, so you should."
"But that thinking's off. I reckon over 50 per cent - probably much more couldn't name one of my albums, let alone say they've bought a ticket to a show. They're no more fans of me than they are of the Leaning Tower of Pisa or Big Ben. They're fans of fame ..."
Robbie went on to explain the reasons he might not want to take a picture, then asked people to "let people be people".
"Let people be people. Humans, struggling - like we all are in one way or another. Allow people the dignity of their privacy, their wants, their needs. Because most of us are just trying to protect ourselves, mentally, physically, or both. Just like you."
Williams received support on the post from his fellow celebrities, with Kris Jenner commenting: "Wow, so beautifully said and I really understand this ... thanks for being so brave and vulnerable and for explaining this so thoughtfully and so well ... sending love. God Bless."
Adam Lambert wrote: "This resonates. I think it's helpful to explain it because it's hard for the public to understand what it's like from the opposite perspective. Thank u for this!" and Aimee Lou Wood said: "This is so perfectly put. Planes are particularly intense because you're trapped in the sky."
And, Paris Hilton said: "This made me cry.. love you bro, thank you for being vulnerable and saying how you feel."
With AAP.