When we have a very busy exhibition, as Ai Weiwei is, I like to take a turn on the front desk, not to sell tickets (I haven’t had the training), but to observe the responses and reactions of visitors and what it’s like for staff.   I could scarcely have chosen a trickier morning as we are having to limit the number of tickets sold on the desk to 25 per half hour, owing to the great number of tickets presold online.   What struck me was the infinite patience, tolerance and good humour of those waiting in line, even if they had international flights to catch, and the infinite patience, tolerance and good humour of the person selling tickets in multiple and totally unpredictable combinations.   Then I went to see how Edmund de Waal was doing and was conscripted to take the tickets of visitors myself.