An 18th Century British admiral would never have accepted battle when he had such an inferior force as the English had at the Four Days Battle. Frank Fox's book, A Distant Storm: the Four Days Battle of 1666 provides the answer, as best as it is possible to know. George Monck, by then, the Duke of Albemarle, had decided before ever encountering the Dutch to give battle. He could easily have justified withdrawing, as he knew that reinforcements would soon be ready. The fleet was also reduced due to Prince Rupert being sent to intercept a suspected French raid on Ireland. Instead of withdrawing, Albemarle fought.
The clinching point was as the English came up on the Dutch fleet, they found that the Dutch were anchored. The English had caught the Dutch completely by surprise. Such opportunities seldom are presented. The English swept down on the anchored Dutch fleet. Cornelis Tromp was the first to recognize what had happened. The ships of his squadron cut their anchor cables and set sail, as quickly as possible. The last time I spoke with Frank Fox, he mentioned the Blue flag from the Fighting Instructions. Albemarle used it, in this instance, to mean "fall into line in my wake". After that, Albermarle suddenly ordered the "Bloody Flag" raised on the fore. At that signal, the English ships swept in for an attack. Then the battle started.