unconvincingness

First, that's hardly a demonstration of its alleged stunning unconvincingness.

Carry-Over Thread 2007

After the introduction has given a fantastic account of the Pre-Adamitical world, and explained with elaborate unconvincingness how the manuscript of the book came into existence, the tale commences like a moral allegory, but soon lapses into mere extravagant adventure.

The Life and Romances of Mrs Eliza Haywood Whicher, George Frisbie 1915

The draught from the shiny dark street and square struck cold, and Edwin responsively sneezed; and Darius Clayhanger upbraided him for not having worn his overcoat, and he replied with foolish unconvincingness that he had got a cold, that it was nothing.

Clayhanger Arnold Bennett 1899