The lookup feature works in one direction but not the other because Clay only allows data to be sent in a linear direction (A β B β C). Loops (A β B β A) aren't possible with the "write to table" feature.
If you want to send data back to the original table, you need to use either:
** Lookup Multiple Rows in Other Table
** Lookup Single Row in Other Table
These lookup actions allow you to reference data from any table without creating loops.