Everybody has a love/hate relationship with their abs.  They love working on them and yet hate the pain of planks!  Before someone begins an abdominal routine, it's important to make sure they understand what muscles to focus on.  

Ensuring the right and left sides are working equally is also a good idea.  If they don't, this is where problems begin.  Slowly but surely - one crunch after the next, compensation patterns develop.  The stronger side gets stronger and the weaker side never catches up.  

If one side of your abs is stronger than the other, it causes a subtle rotation and side bend in the spine that will eventually lead to bigger problems then flabby abs...