Some issue may cause chain effect to everyone.
Yesterday I passed some photo to a friend (a), ask him not to pass the photo around, he said ok. Today, I obtained the photo from somebody in the same company. Then I ask him on this. He told me:
He (a) pass -> (b), (b) shared with (c), (c) ask her friend (d) to see. That why the photo being passing around from me to (d). When I knew this information, I have some gentle quarrelling with my friend (a). After that, (a) goto ask (b) why she pass to (c) & (d), then (b) goto ask (c) why (d) have the photo? (c) goto ask why (d) goto inform me about the photo issue.
See? this is so called chain effect…