Anyone who's lost someone to cancer will say this, that you have to struggle to try to remember the person before the diagnosis happened, because they really do change - as anyone would change.
I was trained by Method acting teachers and we were taught that aside from whatever gift you may or may not have or the level of that gift, that you were obliged to know how to build a table. It's a craft. It's like being a ballerina or a violinist.