Well, a few schools of thought believe that at a certain point, you reach
"Enlightenment" , where you are completely at peace and gain a full understanding of life's mysteries.
But personally, I believe that just means moving onto a different stage of PD, where you have new goals and new mountains to climb, some of those may be something that we (i.e. the un-enlightened people) are not able to comprehend.
I don't think the journey ever stops. With personal development, it's all about the journey and the process of learning. I really do feel the more I learn, the less I actually know.