They say we can accomplish anything we put our minds to. Is this true and to what extent. Consider this....?

I already have a degree in a field but I don't think it really taught me that much. I wish to begin study on my own intending to truly become and expert or even an authority on the subject. Can a reasonable human be dedicated and diligent enough to do what's necessary despite the lure of doing more frivoless, pleasent things all the time. I wish to change my life and the only idea I came up with was to study more and change who I am through knowledge. Does this sound extreme or impossible? What are the limits? How do I get myself into the mindset required for this endeavor? Your thoughts?