DiResta had that chance to secure a drive in a top team last year as his stock was decently high and many said he was unlucky to not get picked up... I'm not even sure he'll be on the grid much longer at the current rate.
Depends if his free Mercedes engine tie up continues.
It's not 'bad luck', it's 'second driver syndrome'. Barrichello was a classic sufferer.
The #1 gets the components which are proved to be reliable. Whereas the #2 gets the components which are experimental and possibly a bit flaky, and pays the price. Rinse and repeat.
Isn't that a bit at odds with some peoples views that Vettel is the one getting all the fancy new clever parts while Webber is stuck with a base line car.