They do not make them like this anymore.
“I've always been skeptical of people who say they lose themselves in a part. Someone once came up to Spencer Tracy and asked, “aren't you tired of always playing Tracy?” Tracy replied, “What am I supposed to do, play Bogart?” You have to develop a style that suits you and pursue it, not just develop a bag of tricks”. - James Stewart.
I once read somewhere that James Stewart quit acting because he no longer liked himself on screen. This makes a lot of sense to me, I need to like my work. It'll never be perfect, but it's important I'm on the right trajectory, in terms of becoming the ideal actor I'd like to be. If I was not on this trajectory, then I would either quit, or fix it.
Now, it's always a shock when I first see myself on screen, because my performance rarely conforms to the idea of the performance I had in my head, nor does it resemble how I felt while I was giving it. If we're dealing with the moment honestly, then our performances never will be how we expected them to be, all sorts of bits and pieces emerge which we had not intended, in fact - it couldn't be how we expected it, unless we impose our ideal on the moment rather than dealing with it as it unfolds, and the truth gets lost. However, once the first shock wears off, we can begin to appreciate our performance for what it is, and calmly debrief from there. Acceptance then, is the first step to improving our work – accept that what we see infront of us is the actual performance we gave. If we get all neurotic about our work, then it will be very hard to progress, because it means we cannot truthfully reflect upon what we've done – we will either repress it and pretend that our performance was ideal, or freak out because our performance was not the ideal we saw in our head. I say forget the ideal we saw in our head, it is a red herring, we should compare what we have done to the needs of the scene instead, to do that is useful and rational.
However, we should also compare our performance to our definition of what great acting is, we should compare it to the actor we are striving to become. Again, this will lead to effective improvement – if, for example, you think you need superb diction in order to be a great actor but you mumble, then you know what you need to do. I thought it strange that James Stewart quit for the reason he did – surely a man who enjoyed one the most glittering careers there ever was, possessed the capacity to fix something he didn't like about his work? After all, he probably didn't get to where he did by being sloppy and lazy. Then it occurred to me that Stewart must have seen something in his work which not only compared unfavorably with his notion of great acting, but that that something must have been beyond his power to put right. He gave his last onscreen performance at the age of 78, so we might conclude that whatever it was, it might have something to do with age, either way, it convinced him he was no longer capable of attaining his great acting ideal.
As Stewart says, you've got to develop you're own style and pursue it – I take this to mean developing your own aesthetic. It's about being an individual creative artist rather than an employee. It also happens to be more pleasurable, meaningful, and fulfilling to work for your own satisfaction rather than trying to please other people, which rarely works anyway, and usually ends up with a loss of self-respect. Define the ideal actor you want to become, and pursue that ideal, and discard anyone or anything which seeks to block that pursuit, and if it's you yourself blocking it, well, then, you know what to do.