As the saying goes - you're telling me!
I believe it's like doing a good piece of work, say a painting, about 80% of the learning and creating goes instantaneously and quickly. The last 20% is the hardest, and the bit that makes or breaks a painting!
Many artists believe one should stop after 80% and not put the last 20% of work in, leave it in the rough, and it certainly would have appeal, but it's that last 20% applied correctly that makes it an unforgettable master piece in my opinion. When it goes from Good to Brilliant.
So what I have experienced in my life is that the majority (80-90%) of most good things/habits once conviction 'sets in' instantaneously, but the last 10-20% goes gradually!
Also, once God got hold of me 80-90% of things changed for the better; it's the last 10-20% that I am struggling with now.
And I am aware of the reality that it might not reach perfection on this earth - why I need God in my life, to make up for my imperfections, and to love me as though I have none.
God Bless - (I am still enjoying this book and your summaries),