妄想

to attempt vainly / a vain attempt / delusion

absurd / fantastic / presumptuous / rash

to think / to believe / to suppose / to wish / to want / to miss (feel wistful about the absence of sb or sth)

to think (about) / to think of; to devise / to think (that); to believe (that) / to desire; to want (to) / to miss (feel wistful about the absence of)

to be carried away by one's wishful thinking (idiom) / to labor under a delusion / wishful thinking

paranoia / megalomaniac

delusional disorder / (fig.) paranoia