Why can an INNER JOIN return fewer rows than either of the joined tables?

An INNER JOIN returns only the rows that have matching values in both tables. If a row in one table has no corresponding match in the other table, it is excluded from the result set. Therefore, the number of rows in the join can be less than the number of rows in either input table. For example, if Table A has 10 rows and Table B has 8 rows, but only 5 rows have matching keys, the INNER JOIN will return 5 rows.