Not really true. Your worth is based on what a company is willing to pay you, which is somewhat based on what the industry/ market determines as the worth of the position you're trying to fill. You can't just go around asking for a six figure salary for a position that doesn't pay six figures at any company, they'd laugh at you.
Also, depending on your field, there aren't that many employers willing to hire anyone, let alone someone that's going to aggressively negotiate their worth when there's currently a sea of people who would take the position for less. So unless you're literally traveling the world to find that perfect employer, which not very many people have the time, money or ability to do, your options are severely limited.
With that said, what you're saying isn't false, it's just a bit of an overstatement on just how much control you have in this situation.
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I promise you they've learned some valuable skills in that time frame. The problem is, many employers won't see it that way. The trick is how you market yourself.
Working in fast food doesn't take much in the way of outside training, but not just anyone can do it well. Anyone might be qualified to, yes, but that doesn't mean they will do well. I'm sure everyone knows someone they work with that is perfectly qualified to be doing their job, but suck at it, because of who they are as a person. I'm also sure everyone has had experiences with people in fast food that are really good at their job, and also with people that are really bad at their job.....how many times have you gotten your order and it's wrong, after taking WAY longer than it should to take your order? Or gone to the same place and been pleasantly surprised that they got everything correct, were able to quickly and accurately take your order, etc...? That's what I'm talking about.