"I do tend to play strong women," she tells the room. "I play different kinds of strong women. I've played dumb blondes, I've played morally bankrupt strong women, I've played good girls, I've played strait-laced straight arrows, I've played wild women, yet they're always strong, and I honestly sometimes feel that's my . . .," she pauses, as a few scribes crane their heads and call out quietly, "calling card?" "strength?," words she ignores and says instead, ". . . Achilles heel, as an actress. I don't really know how to play weak characters. I think if I played a weak character you wouldn't believe me. I think it's the thing I can't get rid of." (emphasis added)
It's somewhat counter-intuitive, I suppose, the idea that your strengths can be your weaknesses, and vice versa; but if you really think about it, it makes a lot of sense. Areas that you are strong in, that you have a natural aptitude in, you also have a tendency to ignore in your training because you can always manage through a combination of natural talent and work. Your weak spots, however, are the areas that you're aware of (hopefully) and always working on.
The difficulty for actors is that when you start getting cast in roles, chances are you're always going to be cast a certain way; because of your look, your sound, your abilities. The majority of actors are like this, playing the same essential character over and over. And that's great, it's possible to have a fantastic career and play a lot of brilliant roles doing that. It's also possible to become a one-note joke. I don't know that there's any real way to avoid it, barring unusual genius and/or weirdness (Kevin Kline, Johnny Depp and Val Kilmer all come to mind); not if you want to get paid, at least. And I guess, to a certain extent, that's what it always comes down to.