''But you can't really lose hope and focus. You've got to focus on what you can control. Work on your strengths and weaknesses, fine tune and make sure you're ready when you get that chance."
Wagner has played 16 tests, taking 58 wickets at 34.48, but his last four have yielded 19 at 27.
When he missed the initial selection for Australia, he knuckled down with Otago, played for New Zealand A against Sri Lanka, and he's happy with his form and delighted to get another chance.
His status on this tour has had a technical change too. He was initially called over as cover for Tim Southee. Mitchell McClenaghan was then named as replacement for the injured Jimmy Neesham.
However Wagner is now a full member of the group, McClenaghan has changed to a covering selection.
The translation is Wagner was always the first choice of the two.
He had a workout at the Melville club in Perth yesterday with McClenaghan and knows the score about bowling at the pacy, bouncy Waca: don't get over-excited.
''I think you can get ahead of yourself and get carried away. You still want to be cool, calm and collected and hit your areas for a long time. The wicket will give enough assistance that if you do that, you'll get rewards," he said.
And the heat doesn't worry him.
''It's quite nice and keeps the body quite loose. It makes that second and third spell a little bit easier. You don't have that stiffness and pain around.
''It is a different challenge, it is going to take a while to adapt to the heat but everybody has played around the world enough that they've experienced that in the past."
There's a suspicion New Zealand may play four seamers in the test, and Wagner, who brings boundless enthusiasm and runs in hard all day, may have his nose in front of Matt Henry and McClenaghan for that fourth spot, supporting Southee, Trent Boult and Doug Bracewell.
