The first combat deployment of the tank was at the Battle of Flers-Courcelette, on the bloody Somme, in 1916. The tanks helped to spearhead British attacks to take a number of German outposts along the line, which had stagnated since July, when the Somme offensive launched. At F-C, the British deployed their new Mark I tanks, the famous rhomboidal tanks we probably associate with World War One. These tanks, used in combination with infantry, were able to successfully reach their objectives and take them. Many Germans found that their weapons were largely ineffective against the advancing behemoths, and either fled their position, or waited for the tank to pass before resuming their defense. Regardless, when used in combination with infantry, the tank was effective at silencing guns and raking trench lines with fire.

However, both before and after F-C, there was tremendous criticism of Douglas Haig, commander of the BEF, and his deployment of the tank. These largely have come from the self proclaimed 'inventors of the tank' Ernst Swinton, Winston Churchill, and their supporters. Their argument roughly runs along these lines: In 1916 the tank was a new, largely unknown weapon to which the Germans had few defenses and little moral preparation. If Haig deployed them in so called 'penny-packets' (small numbers), they would not achieve decisive results, but would tip the Germans off to the presence of a new and potent weapon. Once alerted, the Germans would prepare defenses to counter the technological power of the tank, and would brief their men on how to avoid a moral panic at the sight of a tank. They would go on to argue, especially Churchill, that the deployment of the tank at F-C was just that kind of 'Penny-Packet' attack.

The 50 or so tanks at F-C did cause the kind of technological and moral panic that Swinton and Churchill expected, but it also provoked the expected German reaction. As a result of the battle, the Germans trained their soldiers on how to combat tanks, which included grenades, machine gun fire with new armor piercing rounds, and directed artillery fire, sometimes over open sights. These tactics, once honed, would prove deadly for British tank crews in the coming years.

And what, Churchill would later asked, did the British gain? A few destroyed villages in a sector which had already stagnated. The tank theorists both during the war and after argued for offensive supported by massive numbers of tanks. IN his 'Plan 1919,' JFC Fuller had proposed deploying almost 5000 tanks to destroy the German army. Haig's 50 tanks were seen as too few to achieve any significant result, but enough to tip the British hand as to what they had.

There are some issues with the critical position, especially when you consider how many of these unproven weapons were being called on to be held back (hundreds) to be loosed in one big, but untested and unproven, battle. In 1919, JFC Fuller's tank force had the advantage of three years of training, testing, design, and tactical evolution which had made the British leading tank experts. None of that had existed in 1916. But there is, I think, a kernel of truth in the Churchill criticism, and its a direct answer to your question. At F-C there was a panic over the first deployments of the tank. The Germans couldnt handle the new weapon, and found themselves completely at its mercy, or more specifically the mercy of the infantry which followed. But they quickly recovered and implemented new tactics and technologies which helped to counter the tank, but more importantly helped steel their men against its advance.

Sources:

J.P. Harris, Men, Ideas, and Tanks: British Military Thought and Armoured Forces, 1903-1939

John S Weeks, Men Against Tanks: A History of Anti-Tank Warfare

Christy Campbell, Band of Brigands: The First Men in Tanks

JFC Fuller, Plan 1919