Authors:

So, eventually, he made one final arrangement with himself, which he has religiously held to ever since, and that was to count each fish that he caught as ten, and to assume ten to begin with. For example, if he did not catch any fish at all, then he said he had caught ten fish - you could never catch less than ten fish by his system; that was the foundation of it. Then, if by any chance he really did catch one fish, he called it twenty, while two fish would count thirty, three forty, and so on.

Jerome K. Jerome (2014). “Three Men in a Boat: To Say Nothing of the Dog”, p.297, Diderot Publishing
So, eventually, he made one final arrangement with himself, which he has religiously held to ever since, and that was to count each fish that he caught as ten, and to assume ten to begin with. For example, if he did not