Being focused means not wandering off-topic. Stick to what's important. A good summary highlights only those facts, ideas, opinions, etc., that are useful in helping your reader understand the topic being presented. Avoid a detailed account of the minutia contained in your source material.
Including minute details hinders the reader's ability to understand why the summarized information is relevant to your document in the first place and can lead them to conclude that you may not fully understand your topic.