Ok, this might help paint a picture.
You're midway in a tourney and you've everyone at your table has a decent stack. You get a pair of 5's. Would you push all in? Nope (hopefully). If you have AK in the same situation do you call all in? Nope.
The AK is a slight underdog to the pair but people seem to be more prone to push with it. But you shouldn't anyway.
In both cases why risk your tourney life over a coin flip. Looks daft but people do do it.
Now you're on the short stack in the same tourney later on. The blinds are approx 1/5th + of your stack. Do you push? You have to double up to survive and aces and pairs are 'powerfull' hands to do it with - powerfull in the respect that they can win you a headsup showdown.
The word headsup is important here. Since you want ideally one caller for you double up. If you let your chips bleed away you'll get a few callers. That reduces your survival odds
It's worth noting that when you're pushing you ideally want to be first in the pot with your push. This is because someone already in means you're probably up against a similar hand that stands a chance of being better than yours - you have fold equity if first in.
In my opinion pushing/calling allins have their place but only when they are needed and when the conditions are right. When you're talking participating in coin flips whilst in tourneys, your fighting to stay afloat.
If you have a string of exits because the odds haven't balanced in your favour, that's just unlucky. Math statistical probability is used to model the poker situation and will be correct over a huge amount of hands. You can get a skewed variance in the short terms but it still the correct thing to do since eventually over enough hands it will even out. You can't gaurantee this in the short term.. As an example, I know a chef that invested his life savings into a bookie business that went bust over a series of rediculous outrageous odds races that come in. He simply thought the likelyness this would happen was too extreme and didn't lay off the bet with other bookies. This was within the 1st month of business. Lost everything. I don't see loads of bookies going bust though. They do quite well because the model their risk on Maths effectively. So should you. Same with Casinos
Just out of interest - one last point about luck actually which I think is very important. Only bad luck is visible. You may not be as unlucky as you think you are.
Assume you've just lost to a 3 outer You're able to work it out instantly how bad your luck is and curse that player.
However, you could actually have been lucky NOT unlucky but not seen it. This guy may have hit a 3 outer to stay alive in the tourney, but his all in move may have made someone else fold - where if he remained in could have resulted in you losing your stack because his hand drew out to a monster. This is why people are always inder the impression that they are unlucky in poker. Becasue they only see the bad luck.