Conditioning and control, are always the best factors. Ask yourself two question, can I make this shift tonight? And, do I have the power to control my abilities.
One, get used to the job, make yourself know you can and will make it time and time again. Strength has nothing to do with it. Its about how bad you want it and / or willing to make the impression to stay around. Its called ethics, yet they can only go so far.
Control is a hard one to master. My father would tell me " sure he can throw the ball 145 mph, but can he get it in the strike zone? ". All so true, control is the hardest thing to master. Its all about showing you have it, and its also about holding your skills at ransom. They pay you to work, not the other way around. They want your skills, their gonna have to pay you and give you seniority.
Btw, preloaders are given a pass on all things. Here, guys get 2 - 6 missloads a night all year long and never get put elsewhere. Its because the job has a huge turn over rate, all the time. Its risking someone new to load a car with 35+ in training, while soups working and people filing and so on. Preload is a waste land, nothing is the same everyday. And yet, its always the last end of all your packages picked up, rts'ed and delivered.