I have seen the word before but I forgot what it is. The word is to describe a mental/emotion of a person when the past experience has given him repeated disappointment on a certain thing. The person is getting used to the feeling and adapt to not expecting the high quality outcome.
The word jaded seems to fit your description.
- fatigued by overwork. EXHAUSTED
- made dull, apathetic, or cynical by experience or by having or seeing too much of something
The second meaning appears to match your exposition.
You could say the person is disillusioned.
As Merriam-Webster's Learner's Dictionary defines it:
having lost faith or trust in something: disappointed that something is not as good, valuable, true, etc., as it had seemed
She became more and more disillusioned with politics