I know differently. The raw material for writing comes from real life, and by real life I mean the life of the writer. We don't 'imagine' it all. Heather Sellers in Page After Page refers to this raw material as compost. Some go so far as to say the label 'fiction' is a misnomer because everything that writers write is taken from their real or vicarious experience.
Sometimes I sit at the computer and chase after ideas. Brainstorming, it's called. What I usually end up with is a drizzle of possibilities, none of which glow and beckon, and they certainly don't storm.
Ideas get me instead. Seemingly from nowhere, but actually from my subconscious as it continually processes the raw material - the compost - of my life, an idea appears, and it is so delectable I have to write it down. These ideas occur in the most unlikely of places: the shower, a management meeting where I really should be paying better attention, in a taxi, and sometimes while I sleep.
By the time anyone emerges from childhood he or she already has a sizeable compost pile that continues to swell and teem as the years pass. Some of it is new, raw and smelly, and we don't want to touch it. Part is quietly rotting down, transforming itself into the rich material of future ideas for stories. And right at the bottom, deep in the subconscious, is the good stuff. We can search for it, or it can announce itself 'out of the blue' - actually through deep associations we barely understand and seldom recognise.
Call it imagination. Call it the subconscious, or the akashic record. Call it whatever you will, but that's where our stories begin. We find them, or they find us, and we cultivate them - painstakingly, painfully at times, lovingly - into those brand new releases that give us so much joy. All we need to do is keep enriching that compost heap of life with new experiences and lots and lots of reading.