My pet peeve with agile is it is so rigid at most places. Our team had a bug a while back. We all failed to understand something until it was getting QA'd. We told the PO that we'd need at least part of a sprint to fix it and asked if we could get that prioritized in the next sprint. You would have thought we'd asked to kill someone. We wasted a couple hours debating why it couldn't be finished in this the last day of the sprint. WTF?