Generally speaking, defensive engagements are easier to fight and offensive actions take higher casualties. I don't think its a coincidence that when Lee was on his strongest offensive action (Gettysburg) that he had his most significant failing.
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Generally speaking, these comments are true. Lee was obviously forced on the defensive in the 2 year end-game with Grant, but his defense was anything but passive and fixed. He kept Grant up at night right until the end. Nor was he ineffective on the offense. I agree that Gettysburg was the singular failure of his career, but even an analysis of that leads to some controversy. He didn't lose it by himself, or by not trying; but even after the epic failure of Pickett's charge the Confederate army walked away with 3,000 less casualties than the larger Union army suffered on the defensive. I guess you know where my vote lies.