Student or Learner
Please help me understand the following in bold in easy English?
1. It is difficult for a writer to admit being without words, but that is precisely the case when I try and express what the project of writing this book has meant to me.
2. Dr. Decosterd's expertise in human behavior, the brain, and learning applied to a leader's personal best is a refreshing and powerful combination.
In the above, what does "applied" modify, learning or expertise? And please explain what the part in bold means.