Balsa Grain Direction?

Eugenio Cebollero posted this on the Scratch Built Rocketry and Rocket Repairs Facebook page: 

"When scratch building and making ones own fins from balsa stock one must always remember to pay close attention to wood grain direction. I stole this from a woodworking group and this illustration perfectly explains the importance of grain direction as it correlates to strength."

My response: "That grain is gonna be hard to fill." 

Eugenio responded: "Nah, that's what the dip is for!"