This is precisely why I am not entirely in favor of keeping magickal diaries. I believe that they can be useful. Many experiences can be forgotten over time, and in particular details can change. There can be great value in recording such experiences for others to study or to invite suggestions or discussion. But there is also a risk of placing the memory of one's experiences entirely into the text. In that case, one forgets the experience and remembers only the text, or the surrogate experience provoked by rereading the text.
I also have a collection of Russian folktales in which a wicked old man places his mortality in an egg or some other delicate object, and then hides the egg away. He is then immortal unless someone breaks the egg. The protagonist, for whatever reason, has to kill the old man, therefore he must find the egg.
In the case of a magickal diary, those memories have a greater potency than ordinary memories. To capture them in a text and then lose their essence would be a more vital loss. Just as we no longer need to remember as much as we did before writing and the printing press, an individual would no longer need to remember, and hence internally process, his or her 'magickal' experiences to the same degree.