clarify

Author: dwight

source/reference/command/replSetSyncFrom.txt

@@ -16,11 +16,11 @@ replSetSyncFrom
    which host the current :program:`mongod` will poll :term:`oplog`
    entries from. This operation may be useful for testing different
    patterns and in situations where a set member is not syncing from
-   the host you want. You may **not** use this command to force a
-   member to sync from:
+   the host you want. The member to sync from must be a valid sync 
+   source for data in the set; that is, it it cannot be:
 
-   - itself.
-   - an arbiter.
+   - the node itself.
+   - an arbiter (arbiters have no data).
    - a member that does not build indexes.
    - an unreachable member.
    - a :program:`mongod` instance that is not a member of the same
@@ -54,8 +54,7 @@ replSetSyncFrom
 
       :dbcommand:`replSetSyncFrom` provides a temporary override of
       default behavior. When you restart the :program:`mongod`
-      instance, it will revert to the default syncing logic. Always
-      exercise caution with :dbcommand:`replSetSyncFrom` when
-      overriding the default behavior.
+      instance, or if the sync's TCP connection flaps (resets), mongod 
+      will revert to its default logic for selecting a sync source.
 
    .. slave-ok, admin-only