Oracle explanation plan: cardinality returns a huge amount, but the query does not return records

I wrote a complex oracle sql query, and the statistics of the explanation plan looks like this: Cost: 209,201 Bot: 187,944,150 Capacity: 409,675

Now the database administrator has configured the query, and the statistics are as follows: Cost: 42,996 bytes: 89,874,138 Number of Carl: 209,226

My first question is: if the numbers are lower, does that automatically mean better performance? Which number is the most suitable? Cost / power / bytes? My second question: I understand that the number of rows is the number of rows. But when I run the query, it returns the string "0"! I got the impression that the cardinality should be the same for two queries that should return the same result sets. Think this is wrong?