I learned something of magnificent value from this book. The heart of this book is a family drama, and it comes to focus on two brothers and their father. For many months and years of their lives, conflict is building. Anyone reading the book can tell you the central problem. It's a bit of unrevealed information, and I won't spoil it for you. The reader knows the whole time that someday, somehow, this information will be discovered. Along the way, the characters face other kinds of problems and conflict.
Here's what Steinbeck does that would not have occurred to me: The other problems are handled and do not turn into horrible disasters. Not every negative event is a giant drama. They are dealt with and settled, just the way they are in real life. This is a family, and families have problems. They do not shatter with every conflict. For the Trask family, life goes on. For the reader, we get a sense of their closeness, their reality, and what they are willing to do for one another.
Guess what happens when the final conflict arrives? We are staggered by the possibility that this family— which has been through so much and stayed together— might fall apart. Steinbeck, while keeping our interest with constant conflict, has also lulled us into believing that these folks can get through anything. Then suddenly that is in doubt. Do they manage, one more time? Not tellin'.