A person who genuinely wants something for himself or herself should have no problem or guilt about saying that they want it, without any mention of the word 'deserve.'

Earning, as it were, is a concept that involves multiple parties. One person does the work. The other person rewards that work. That is what 'earning' is. It is someone external to yourself showing appreciation for what you have done by rewarding you for it.

To say, "I deserve," implies that there is some sort of pre-agreed scoring system to determine whether or not the thing wanted has been earned.

To say "I deserve" is almost like having an invisible friend that only you can see, and that's exactly the image that pops into my head when I hear someone use that expression. My mind immediately tries to conjure up the second person in this arrangement who supposedly promised something to the person claiming to 'deserve' it. However, often, as the person continues to talk, I slowly realize that they, themselves, are both people in the deal.

I consider it a reliable indicator of mental illness.

Not only is the person uncomfortable with having things outright, for some unexplained reason, without attaching to it some artificially-rigged illusion of a multi-party compensation scheme.

In the end, if they get frustrated enough, they will psychologically 'knife' that invisible other person (whose approval was so indispensable only moments before), out of sheer frustration because that invisible person somehow became too demanding or unreasonable.

And. The. Whole. Time. There. Was. No. One. Else. There.