Books I have read are unthreatening, placing no pressure on me and offering the comfort of a familiar experience. In contrast, unread books are not so relaxing - some bring back memories of unwise purchases or over-eager review copy requests, some have remained unread because they seem difficult or daunting, and even the most docile of them whisper an insistent "read me! read ME!".
With 3000+ books, deciding which books would go into storage and which would be shipped to the UK can't be too drawn out a process. So my basic rule has been simple: if I've read it it goes into storage and if I haven't it goes to the UK.
This means that my study, previously a congenial four-fifths old friends to one fifth strangers, is steadily becoming more foreign and less comfortable.