Kowitz v. Trinity Health, "In determining whether an employee is a qualified individual under the ADA, essential functions are the fundamental duties of the job, but not its marginal functions; in determining whether a job function is essential, courts consider several factors, including what functions the employer thinks are essential, written job descriptions, how much time an employee spends on the job performing the function, the consequences of not having the employee perform the function, and whether other current employees in similar jobs perform the function."