Roots.

"What are the toughest, hardiest plants in a time of drought? The ones that put down the deepest roots. In fact, farmers sometimes stress certain varieties of trees, depriving them of water for weeks after they are planted, in order to force those trees to put their roots down deep into the soil When those trees are mature and times of drought and hardship come, they will survive, while trees with shallow root systems are scorched to death by heat and drought.

That is what hardship does in our lives: It forces us to put our roots down deep into the soil of God's love."

- Let God be God by Ray Stedman