Select * from users WHERE upper(lastName) = upper('Pringle') - Mailing list pgsql-jdbc

I have notices that when you want to use the upper() function, you must also
use the trim().

For example,
In a situation where a column names lastname is char(40):
SELECT * FROM users WHERE lastname = 'Pringle'   returns one row.

SELECT * FROM users WHERE UPPER(lastname) = UPPER('Pringle')   will return
zero rows.

SELECT * FROM users WHERE TRIM(UPPER(lastname) = TRIM(UPPER('Pringle'))
will return one row.

This seems odd to me.  Can someone explain?