See Fair Work Act 2009 s.387(a)
'[T]he reason for termination must be defensible or justifiable on an objective analysis of the relevant facts.' It will not be enough for an employer to say that they acted in the belief that the termination was for a valid reason.
The valid reason for termination is not to be judged by a legal entitlement to terminate an employee, 'but [by] the existence of a reason for the exercise of that right' related to the facts of the matter.
The Fair Work Commission does not 'stand in the shoes' of the employer but will need to be satisfied that the termination of the employee was for a valid reason.
It would be harsh, unjust and unreasonable for an employer to dismiss an employee summarily on the ground of serious misconduct without taking reasonable steps to investigate the allegations of misconduct and give the employee a fair chance of answering them.
It is the reason or reasons for the act which must be discerned. An investigation of the reason or reasons for the act will involve, as a matter of meaning and language, an enquiry into the explanation for the act or why the act was done.
Findings made by an inquiry established by the employer will be relevant to the Commission's determination of the issues before it provided it is established that:
An employee is entitled to both substantive and procedural fairness in respect of a dismissal. Substantive fairness will be satisfied if the grounds upon which dismissal occurs are fair grounds. Broadly speaking a dismissal will be procedurally fair if the manner or process of dismissal and the investigation leading up to the decision to dismiss is just.
Where the dismissal is based upon the alleged misconduct of the employee, the employer will satisfy the evidentiary onus which is cast upon it if it demonstrates that insofar as was within its power, before dismissing the employee:
A failure to satisfactorily establish any of those matters will probably render the dismissal harsh, unjust or unreasonable.
 Selvachandran v Peteron Plastics Pty Ltd  IRCA 333 (7 July 1995), [(1995) 62 IR 371 at p. 373].
 Miller v University of New South Wales  FCAFC 180 (14 August 2003) at para.13, [(2003) 132 FCR 147].
 ibid., at para. 64. See also Walton v Mermaid Dry Cleaners Pty Limited  IRCA 267 (12 June 1996), [(1996) 142 ALR 681 at p. 685].
 APS Group (Placements) Pty Ltd v O’Loughlin  FWAFB 5230 (Lawler VP, O’Callaghan SDP, Roberts C, 8 August 2011) at para. 33; citing Toben v Jones  FCAFC 137 (27 June 2003) at para. 151.
 Australia Meat Holdings Pty Ltd v McLauchlan Print Q1625 (AIRCFB, Ross VP, Polites SDP, Hoffman C, 5 June 1998); citing Bi-Lo Pty Ltd v Hooper (1994) 53 IR 224 at pp. 229–230.