Fred imagined
Thirteen year old Fred could imagine his future so clearly he knew it would come true.
There was a shop, full of bright colours, surprises and noise. There was a lot of laughter. And a lot of money too – he understood enough of his parents' struggles to know that mattered.
And, of course, there was George. George and him together, as they always were, as they always would be. (He supposed there would be wives and children too, but they were hazy in his imagination.)
The important thing was The Weasley Twins working together forever. Fred knew it would happen.