NFL organizations try to prepare for every possibility, but surprises always occur. These surprises can be positive or negative. Sometimes, they're both.
An injury could lead to an opportunity for another individual, who shines when thrust into the lineup. Or an opportunity could arise when a player is benched or departs. Maybe someone simply outperforms expectations.
A year ago, Ryan Tannehill was a failed first-round pick expected to serve as Marcus Mariota's backup after being acquired via trade. Mariota struggled, Tannehill became the starter and the Titans thrived as the 31-year-old signal-caller led the way.