Answer:
You need to comply with the license terms if what you are doing would otherwise require permission from the rights holder. If your use would not require permission from the rights holder because it falls under an exception or limitation, such as fair use, or because the material has come into the public domain, the license does not apply, and you do not need to comply with its terms and conditions. Additionally, if you are using an excerpt small enough to be uncopyrightable, the license does not apply to your use, and you do not need to comply with its terms.
However, if you are using excerpts of CC-licensed material which individually are minimal and do not require license compliance, but together make up a significant copyrightable chunk, you must comply with the license terms. For example, if you quote many individual lines from a poem across several sections of a blog post, and your use is not a fair use, you must comply with the license even though no individual line would have been a substantial enough portion of the work to require this.