In February 1916, the Germans might have captured the fortress of Verdun (France), quickly through an all-out assault. Instead, the German General Falkenhayn initially elected to make an artillery attack on it, without using a lot of infantry. His rationale was allegedly stated in his Christmas (1915) memo to the Kaiser (some historians dispute this), which was interpreted to mean that he wanted to attack a city of sentimental value to France, "suck in" as many French troops as he could, kill as many as possible with artillery fire, and bleed the French army to death. Capturing the fortress would be of secondary importance. The end result was that the Germans failed to capture the fortress, and inflicted French casualties at rate of only slightly more than 1- to 1 (versus a 5 to 4 overall Allied advantage), meaning a tactical defeat for Germany.
In 1942, the German summer offensive (Fall Blau) started spectacularly with the capture of Voronezh on the Don by the left flank of the southern front by armored divisions. If this armor had been sent southeast to Stalingrad, supported by an eastward advance of infantry, the Germans might have captured it by late July.
Instead, the Germans sent the armor from Voronezh due south for the Caucasus oil fields. This not only prevented them from using the armor to capture Stalingrad, but blocked the infantry advance of Paulus' Sixth Army. The assault on Stalingrad didn't begin until late August, giving the Soviets more time to reinforce the city.
Why were the Germans so dilatory on their attack on Stalingrad? Were they trying to "suck in" Soviet reinforcements to "Stalin's city," destroy them en masse, and thereby weaken Soviet forces to the north (around Moscow) and south (the Caucasus)?