There is a tendency for advocates, consciously or subconsciously, to divide documents and authorities between ‘mine’ and ‘theirs’. ‘My’ documents are those that come from my client, or are helpful to him. ‘Their’ documents are those that come from the other side, or that are helpful to them.
This is natural enough, but it is a mistake.
In most cases it is impossible to divide all the documents in this way. At least some will contain material useful – or harmful – to both sides. If you try to divide them up, you risk missing the bits in ‘their’ documents that help you. You will also miss the bits of ‘your’ documents that help them. This will hamper your ability to present the case.
This point is also true of authorities. Often a party will cite an authority that actually helps the other side. Sometimes this is because the advocate has a duty to bring up a relevant case, even though it doesn’t help him. But it happens surprisingly often in other circumstances as well. Similarly, often an authority will be broadly helpful to you, but contain a limitation or warning that is not. If so, you need to spot it, so that you can deal with it.