Discovery deadlines exist for a reason. Although there are exceptions to every rule – and often a rule dictating how to handle such exceptions – litigants in federal court are expected to show their evidentiary cards in a timely, orderly fashion that avoids surprise. In the context of expert discovery, this means inter alia that witnesses who have been retained specifically to offer expert opinion testimony must author a written report (i.e., a Rule 26 report) setting out their opinions and the bases for those opinions. Fed. R. Civ. P. 26(a)(2)(B). Opinions that are inadequately disclosed may be excluded at trial. Fed. R. Civ. P. 37(c). In some cases, this can leave a litigant unable to make a prima facie case and survive summary judgment.