1. When you have absolutely nothing in common other than eating breakfast together, but it was such a spectacular breakfast that you know in future years you will be able to bond instantly, after years apart, over the memory of it.
2. When you are united by a densely interlinked set of flaws and inadequacies which slot into each other just so, leading every now and then to the sort of planetary alignment when all involved can do great things.
3. When you can all do something almost entirely inconsequential, such as wriggling your ears, in an era when there is suddenly and joyously an ear-wriggling record attempt.
4. When you are united by your common love for a thing, and that love has grown big and old and comfortable like an armchair, cushioning all of your other views from each other.
5. When you feel a cosy sense of belonging from reading the updates of a group of people each day, and although you realise that those people mainly do not know you and mainly do not know each other, nevertheless they are a group that you have made, are part of, and love.
6. When you are not yet aware that you are a member of a group, and will not find out until it is probably too late.
7. Groups that you belong to because you would like to belong to them, and for no other reason.