Wishful thinking to the point of lunacy
Example Scenario: PersonA wants to do something, but is told they can't. They're persistent, and they quiet down eventually, but then they find just the slightest justification and jump back into hours-long pleading again as if the past conversations never happened.
I could say that PersonA is a wishful thinker, but "wishful thinking" doesn't necessarily have a negative connotation. PersonA in this case is a wishful thinker to the point of lunacy. Is there a single word or phrase that accurately describes this so that even when heard out-of-context it would be understandable? Optimally it'd be workplace-appropriate, but it's fine if it's not.
Solution 1:
A common phrase that describes this sort of behavior/thinking is delusional optimism, and I found several examples of it used in a business context. Here's one:
When forecasting the outcomes of risky projects, executives all too easily fall victim to what psychologists call the planning fallacy. In its grip, managers make decisions based on delusional optimism rather than on a rational weighting of gains, losses, and probabilities. They overestimate benefits and underestimate costs. They spin scenarios of success while overlooking the potential for mistakes and miscalculations. As a result, managers pursue initiatives that are unlikely to come in on budget or on time—or to ever deliver the expected returns.
That same article quoted from also uses the term overoptimism, but I think delusional optimism has more "punch."
[Source: Harvard Business Review, July 2003, "Delusions of Success: How Optimism Undermines Executives’ Decisions" by Dan Lovallo and Daniel Kahneman]
Solution 2:
Consider the word quixotic.
It suggests wishful thinking to the point of lunacy in pursuit of one's ideals.
The novel Don Quixote is about an old man who decides to become a knight even though the days of chivalry had ended long ago. Despite the impracticality of the notion and a great deal of failure and pain, he still continues to attempt to pursue knighthood (and continues to fail over and over again).
The only catch is that this word is typically only applied to a person pursuing a noble but impractical or impossible cause, so you would not typically use this word to describe a persistent bank robber. Be sure to take the context into account when deciding if this word is right for your situation.
Solution 3:
The idiomatic phrase grasping at straws may convey the concept
- trying to find some way to succeed when nothing you choose is likely to work
Jerry, grasping at straws, searched the backup tapes from last week, looking for the missing files.
- trying to find reasons to feel hopeful about a bad situation
She thinks he might still be interested because he calls her now and then but I think she's clutching at straws.
Cambridge Dictionary of American Idioms cited at thefreedictionary.com
The term flail is also sometimes used
To make energetic but aimless or or ineffectual efforts:
As the end of law school approached, Hill flailed briefly in numerous professional directions
American Heritage
Supplement: Along the lines of the good answer by @pyobum, the phrase cockeyed optimist is sometimes encountered. Merriam-Websters Learners' Dictionary offers this definition of cockeyed
crazy or foolish
Where did you get those cockeyed ideas?
She is full of cockeyed optimism.
The term is the title of a featured song in the musical South Pacific
Solution 4:
Delusional (both definitions from Merriam-Webster):
"A persistent false psychotic belief regarding the self or persons or objects outside the self that is maintained despite indisputable evidence to the contrary; also : the abnormal state marked by such beliefs"
[in] Denial:
2: "refusal to admit the truth or reality (as of a statement or charge) (2) : assertion that an allegation is false"
6: "a psychological defense mechanism in which confrontation with a personal problem or with reality is avoided by denying the existence of the problem or reality"
"in denial" : "refusing to admit the truth or reality of something unpleasant"
Solution 5:
Possibly relevant:
MW: Monomaniacal
"excessive concentration on a single object or idea"