That's not always true. It might seem like it is easier to be careless, but if we're talking about any item over just a couple pounds in weight, you're going to hurt yourself being careless as opposed to being cautious.
There is a monumental difference between throwing 20lb packages all day vs. picking them up and setting them down. Your body will tell you that it's just not sustainable in the long run if you want to live without persistent pain. You can very easily learn this by observing anyone who's done the job for more than a year or two - they might look like they're being lazy but they are really just trying not to hurt themselves. You might throw one or two in anger, but repeatedly throwing packages for 8 hours a day, 5 days a week for 48 weeks will make you regret it. There is nothing more painful and hopeless on the job than a mechanical injury you feel in every single box you move. You learn to do it without hurting yourself and this almost never involves being careless with the package. The consequences might not come from being reprimanded about broken items, but it will come in the form of injury and pain.
I'd say being "careless" means dropping that 60-80lb package to the floor instead of gingerly doing a squat with it, even 10 of those a day and your back will thank you unless you have impeccable form. "Use existing equipment" - perhaps a familiar phrase, one that protects your joints but not necessarily the packages.
There is a monumental difference between throwing 20lb packages all day vs. picking them up and setting them down. Your body will tell you that it's just not sustainable in the long run if you want to live without persistent pain. You can very easily learn this by observing anyone who's done the job for more than a year or two - they might look like they're being lazy but they are really just trying not to hurt themselves. You might throw one or two in anger, but repeatedly throwing packages for 8 hours a day, 5 days a week for 48 weeks will make you regret it. There is nothing more painful and hopeless on the job than a mechanical injury you feel in every single box you move. You learn to do it without hurting yourself and this almost never involves being careless with the package. The consequences might not come from being reprimanded about broken items, but it will come in the form of injury and pain.