It's long been said (with a lot of truth) that "no military plan survives contact with the enemy." But many of the reasons have nothing to do with the soundness of the plan. Leadership failures are the major problem. And it doesnt have to be poor leadership by the commanders of combat units that will doom a plan, the troops moving supplies and equipment can screw up enough so that the fighting units find themselves without essential weapons and equipment at critical times. Consider some of the common leadership flaws among support troops (especially supply and maintenance) that doom otherwise sound plans; 

@ Not making sure that everyone gets the word. Sometimes these are communications problems (someone has a broken or unreliable radio), or simply forgetting to tell everyone all the information they need.

@ Bad maps. American troops have long had a problem with maps, both with reading them correctly or having the right ones when they need them. 

@ Trucks that are not loaded on time, are loaded with the wrong stuff, are not ready to move out when they are supposed to or have accidents because of tired or poorly trained drivers. 

@ Trucks, often carrying essential equipment, or armored vehicles, don't make it because the driver neglected to top off the gas tank before departing or because poor maintenance caused a breakdown. 

@ Traffic jams when two units try to use the same road at the same time. This usually happens because of bad maps, not maintaining convoy speed or misinterpreting instructions. 

@ Unit leaders unfamiliar with the mission and terrain (not paying close attention during a briefing will do that) cause all sorts of timing and coordination problems.

The problems caused by support units not being where they are supposed to be when they are expected can have a snowball effect. Even one support unit, like a few trucks with tank fuel or ammunition, not arriving on time can have a ripple effect. The tank or infantry unit may have to proceed without adequate fuel or ammo and fail in an operation it should have succeeded at. This can cause a ripple effect, as enemy units begin to show up in places they were not expected to be. It's the old "a chain is only as strong as its weakest link" problem, and in modern combat it applies to combat and combat support units.