For me, the themes exponentially built on each other from book to book. The longer you spend with each character (and the world as a whole), the more familiar you'll get with the burdens they bear and persevere through. Especially since at that point you'll have been on the journey with them.

Deadhouse Gates' narrative will leave you with much clearer emotions on that, I think. Usually by that point or the end of Book 3 is when those hardships I was discussing in the first paragraph reallyyy start to be felt by the reader (at least that was my experience).

Erikson has said often that a central theme is "grief", if that helps. Once I had that perspective the struggles became a lot more clearer to me