If you’ll believe in me, I’ll believe in you.

Be 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.

One can't believe impossible things.

Why, what a temper you are in!

Epithets, like pepper, Give zest to what you write; And if you strew them sparely, They whet the appetite: But if you lay them on too thick, You spoil the matter quite!

She felt a little nervous about this; 'for it might end, you know,' said Alice to herself, 'in my going out altogether, like a candle. I wonder what I should be like then?' And she tried to fancy what the flame of a candle looks like after the candle is blown out, for she could not remember ever having seen such a thing.

Be who you are, said the Duchess to Alice, or, if you would like it put more simply, never try to be what you might have been or could have been other than what you should have been.