IME, it's damn hard to do
well.
It sounds easy in the abstract, but there's a lot more to it than memorizing/delivering lines.
For example, it's a bit harder to deliver lines you have memorized when you're also receiving direction that includes communicating an emotion with your facial expression while delivering a specific set of hand gestures that have to be coordinated with the words you are saying, and on top of that, deliver your lines in an accent that you have to maintain throughout, one that is not a natural accent for you. That's all in a day's work for someone like Meryl Streep. (It's beyond cliche to cite her as an example, I realize... but she is in fact quite good at her trade.)
I used to make fun of "bad actors" quite a bit -- and then I tried doing it for myself. It just ain't as easy as it looks/sounds. I'm sure like everything else, it gets easier with time, experience and training. For some people it probably comes way more naturally too, and they don't struggle with it as much as a hack like me.
And yeah... LAJ has some work to his credit. He can tell you all about how easy it definitely
isn't to crack into the field professionally, too.