'Cos by the time you get to 100k, whatever you were doing that got you from 25 to 100 has stopped working. Well, just kidding, but I'm sure there's some truth to that.
For the same reason most find it impossible to turn 25k into 100k; fear... I My guess would be that you have become overly conscious of your initial feat, so much so, that your ego has become somewhat inflated and your mind has created the image of yourself as a "great" trader, or even just a competent one. Either way, any evidence to the contrary is going to cause pain, which overtime will manifest itself in fear. Fear that you cannot live up to the illusion your mind has created of "you the trader". Nothing scares a human so much as the possibility that the mask he has created for himself may one day get ripped off and he might one day have to face his "true self" in the mirror.
My advice; act as if failure is not even in the realm possibility and when you prevail act as if you hadn't...
Perhaps for the same reason that it is easier to walk on a plank of wood that is on the ground than it is to walk on the same plank if it were, say, 50 feet off the ground.
Well it obviously is for one person or he would not have started a thread to ask the community for their opinion. Some find they have a lot more to lose after they have accomplished something then when they started out and in most cases it goes far beyond just monetary loss...
All that with the assumption that whatever method you are using is still viable in the current market environment of course...