Why is my job like the "Dilbert" comics?

I was reading over my collection of "Dilbert" comics again recently, funny how the comic on top of the stack reminded me of recent incidents at my workplace. The basis of this particular comic strip is that Dilbert's boss asks Dilbert to help a co-worker with his project. Dilbert asks, if his co-worker succeeds who will get credit for the project. Answer: your coworker will get credit, it's his projects. Consequently, if it fails, it will be your fault for not helping him enough. Dilbert also decides that if he spends too much time helping his co-worker his own project will fail.

At the same time that I was reading this comic, I was thinking about my boss and his set of demands for me. I feel like my responsibilities are never ending, not only I am responsible for sales, opening credit cards, selling merchandise in advance of sales, but I am also responsible, almost always, for training new employees, merchandising, and helping co-workers whenever they have problems. Can you believe that not only do I have to solve my own customer problems but I have to help my-workers solve theres and just because I happen to be good at it.

Usually my boss asks my to do something, for example calling customers for upcoming sales ("monumental waste of time" I think and my co-workers say). So I will begin calling, and then things will happen that stop me. I will have customers in the store that I need to help, or a co-worker will have a customer problem and ask me for help. Once you get involved in solving a customer problem you have to see it through to the end; some take minutes to solve and others take a couple of hours.

Then, just when I finally get back to calling customers, my boss will show up ask me why I am not done calling about 10-12 pages worth of customers which works out to be about 100-120 people. I will explain to him that I got caught up in other things, I will be specific about it, and then when review time rolls around I will get a mediocre review even though I absolutely went above and beyond my job description. My boss will admit that it is true, and wish me better luck next time on my review and a successful three months ahead until I get my next review. I am already thinking about reviews next week, I wonder how mediocre this one will be?