Hex.3 at left is Thunder below Water
Hex.50 at right is Wind below Fire.
They are total opposites, hex.3 is the first beginning of things, hex.50 is the final result, the state with its laws and structure. Trigram Water is formless, trigram Fire is form and order. But every start is made for a completion and every completion was once started.
The names shows their difference. The oldest form of Tun is a seedling sprouting, the oldest form of Ding is a cauldron.