Something demoralizing is the thing that does this to you — a score, a comment, a week of bad luck that makes you want to stop trying. “The result was demoralizing.” It describes the cause, not the person. A demoralizing speech leaves people smaller; a demoralized listener is the one who feels it. Teachers and managers should handle the word with care: calling a task demoralizing names the harm, not the student. It is a fairly formal adjective; friends more often say “that really knocked me down.”