On poetry and memories, Tarkovsky in his book "Sculpting in Time" says:
"... All four dreams, too, are based on quite specific associations. The first, for instance, from start to finish, right up to the words, 'Mum, there's a cuckoo!' is one of my earliest childhood recollections. It was at the time when I was just beginning to know the world. I was four.
Generally people's memories are precious to them. It is no accident that they are coloured by poetry. The most beautiful memories are those of childhood. Of course memory has to be worked upon before it can become the basis of an artistic reconstruction of the past; and here it is important not to lose the particular emotional atmosphere without which a memory evoked in every detail merely gives rise to a bitter feeling of disappointment. There's an enormous difference, after all, between the way you remember the house in which you were born and which you haven't seen for years, and the actual sight of the house after a prolonged absence. Usually the poetry of the memory is destroyed by confrontation with its origin.
It occurred to me then, that from these properties of memory a new working principle could be developed, on which an extraordinarily interesting film might be built. Outwardly the pattern of events, of the hero's actions and behaviour, would be disturbed. It would be the story of his thoughts, his memories and dreams. And then, without his appearing at all - at least in the accepted sense of the traditionally written film - it would be possible to achieve something highly significant: the expression, the portrayal, of the hero's individual personality, and the revelation of his interior world. Somewhere here there is an echo of the image of the lyrical hero incarnate in literature, and of course in poetry; he is absent from view, but what he thinks, how he thinks, and what he thinks about build up a graphic and clearly-defined picture of him. This subsequently became the starting-point of Mirror.
The way to this poetic logic, however, is fraught with adversity. Opposition awaits you at every turn, despite the fact that the principle in question is quite as legitimate as that of the logic of literature or dramaturgy; it is simply that a different component becomes the main element in the construction. One is reminded here of that sad dictum of Hermann Hesse: 'A poet is something you are allowed to be, but not allowed to become.' How true!"