とうてい到底toutei
1.
An expression used to emphasize the impossibility or futility of a situation, often in conjunction with negative phrases, suggesting that no matter the effort, success cannot be achieved.
2.
A term that indicates the ultimate conclusion or end result of a situation, often used to highlight what is inevitable despite previous attempts or circumstances.
3.
A way to convey profound disbelief regarding the feasibility of an action or event, reinforcing that achieving it is entirely out of the question.
Example:
あなたの話は到底真実だと思えない。