When I first started playing basketball as a teen, my friend Tim and I always discussed who would be the starters in our recreation league games.
Often, neither of us was a starter. But Tim had a great mentality abut it:
"Once I get in the game, I'll play so well that I'm not coming out."
It's the same way with anything else.
The starting quarterback gets injured, and the backup plays so well that the starter loses his job (Tom Brady did this).
The boss is out for a week, and someone steps up and does such a great job, they go and find a place to be the #1 person full-time.
The group needs someone in an emergency situation, you're called on, and you perform at a level that no one -- including you -- thought you could. Noe you have a new performance standard.
You will eventually get a shot -- it may not be the shot you wanted, and it may be a very short shot at that -- but it's a shot nonetheless. Play so well that you can't be taken out of the spot.