How to explain the execution path of this Cypher query? - graph

Question

Imagine the following graph:
And this query:
MATCH(p:Person {id:1})
MATCH (p)-[:KNOWS]-(s)
CREATE (p)-[:LIVE_IN]->(:Place {name: 'Some Place'})
Now, why five LIVE_IN, Place are created even though s is not involved in the CREATE statement? is there any place in the docs that explain this behavior?
Note: this is not about MERGE vs CREATE, although MERGE can solve it.
EDIT: In response to #Tomaz answer: I have deliberately placed MATCH (p)-[:KNOWS]-(s) in the query and I know how it will behave. I am asking for found explanations. For example, is CREATE will execute for each path or row in the matched patterns regardless of the node involved in the CREATE? what if you have complex matched patterns such as, disconnected graph, Trees...etc?
Also note that the direction of relationship KNOWS (- vs ->) will effect the number of returned rows (9 vs 1), but CREATE will execute five times regardless of the direction.
Update:
I have added 3 other node Office and issued the following query:
MATCH(p:Person {id:1})
MATCH (p)-[:KNOWS]-(s)
MATCH (o:Office)
CREATE (p)-[:LOVE]->(:Place {name: 'Any Place'})
And as result: 15 LOVE Place have been created, so it seems to me that cypher performs Cartesian Product between all nodes:
p refer to 1 nodes, s refer to 5 nodes, o refer to 3 nodes => 1 * 5 * 3 = 15
But I can not confirm this form neo4j docs unfortunately.

Answer 1

This is because the Person with id 1 has five neighbors.
In your query you start with:
MATCH(p:Person {id:1})
This produces a single row, where it finds the node you are looking for.
The next step is:
MATCH (p)-[:KNOWS]-(s)
This statement found 5 neighbors, so your cardinality or number of rows increases to five. And then you run a create statement for each row, which in turn creates five Places. You could for example lower the cardinality back to 1 before doing the CREATE and you'll create only a single place:
MATCH(p:Person {id:1})
MATCH (p)-[:KNOWS]-(s)
// aggregation reduces cardinality to 1
WITH p, collect(s) as neighbors
CREATE (p)-[:LIVE_IN]->(:Place {name: 'Some Place'})
When doing cypher query, always have in mind the cardinality you are operating.