To the Looking-Glass world it was Alice that said 'I've a sceptre in hand, I've a crown on my head. Let the Looking-Glass creatures, whatever they be… - Lewis Carroll

He's dreaming now,' said Tweedledee: 'and what do you think he's dreaming about?'
Alice said 'Nobody can guess that.'
'Why, about YOU!' Tweedledee exclaimed, clapping his hands triumphantly. 'And if he left off dreaming about you, where do you suppose you'd be?'
'Where I am now, of course,' said Alice.
'Not you!' Tweedledee retorted contemptuously. 'You'd be nowhere. Why, you're only a sort of thing in his dream!'
'If that there King was to wake,' added Tweedledum, 'you'd go out — bang! — just like a candle!

"what you would seem to be" — or if you'd like it put more simply — "Never imagine yourself not to be otherwise than what it might appear to others that what you were or might have been was not otherwise than what you had been would have appeared to them to be otherwise."

For, you see, so many out-of-the-way things had happened lately, that Alice had begun to think that very few things indeed were really impossible.