从陌生到熟悉一步之遥从熟悉至陌生一念之差
[cóng mò shēng dào shú xī yī bù zhī yáo cóng shú xī zhì mò shēng yī niàn zhī chā]
Suggests how quickly or easily relationships between people can shift. A small action can bring strangers closer ('a step away'), but a single bad thought/decision can distance acquaintances far apart again ('one slip')