I Ching hexagram 16
Hexagram 16: Yu
Enthusiasm · 雷地豫 · Thunder above, Earth below
Enthusiasm and harmony can carry a group into action, as long as nobody gets carried away.
What this hexagram is about
Everyone is in good spirits and ready to move, as when a team gets behind a plan. Yu (Enthusiasm) is about the difference between earned enthusiasm and the kind that is only boasting or daydreaming.
A way to think about it
Ask whether the excitement around you has real support underneath it, and what you would still do on a flat day when the mood has gone.
The text, with Legge's translation
Judgment
利建侯行師。
Yü indicates that, (in the state which it implies), feudal princes may be set up, and the hosts put in motion, with advantage.
When people move together willingly, it pays to appoint capable local leaders and to put an army in motion. The judgment is about harmony that makes action easy.
Image
雷出地奮，豫；先王以作樂崇德，殷薦之上帝，以配祖考。
(The trigrams for) the earth and thunder issuing from it with its crashing noise form Yü. The ancient kings, in accordance with this, composed their music and did honour to virtue, presenting it especially and most grandly to God, when they associated with Him (at the service) their highest ancestor and their father.
Line 1 · 初六
鳴豫，凶。
The first line, divided, shows its subject proclaiming his pleasure and satisfaction. There will be evil.
Boasting about your good fortune and your connections is a bad sign. The support behind you is no reason to announce it to everyone.
Line 2 · 六二
介于石，不終日，貞吉。
The second line, divided, shows one who is firm as a rock. (He sees a thing) without waiting till it has come to pass; with his firm correctness there will be good fortune.
As steady as stone, you read the signs early and decide before the day is out. The text approves of that quick, settled judgment.
Line 3 · 六三
盱豫，悔。遲有悔。
The third line, divided, shows one looking up (for favours), while he indulges the feeling of pleasure and satisfaction. If he would understand!--If he be late in doing so, there will indeed be occasion for repentance.
Looking up to someone powerful for the good times to come leads to regret, and putting off the correction brings more.
Line 4 · 九四
由豫，大有得。勿疑。朋盍戠。
The fourth line, undivided, shows him from whom the harmony and satisfaction come. Great is the success which he obtains. Let him not allow suspicions to enter his mind, and thus friends will gather around him.
Others draw their enthusiasm from you, and a lot comes your way because of it. Drop your doubts, and friends come together around you.
Line 5 · 六五
貞疾，恆不死。
The fifth line, divided, shows one with a chronic complaint, but who lives on without dying.
Constant pressure from a stronger rival feels like a lingering illness that never quite finishes you. You survive because your central position holds.
Line 6 · 上六
冥豫，成有渝，无咎。
The topmost line, divided, shows its subject with darkened mind devoted to the pleasure and satisfaction (of the time); but if he change his course even when (it may be considered as) completed, there will be no error.
You are lost in the pleasure and cannot see clearly, even though the thing is already done. If you can change course now, you are in the clear.
Chinese text: the received Zhouyi, public domain. English: James Legge, The Yi King, Sacred Books of the East vol. 16 (1882), public domain. Plain notes written by this site.
Questions
I cast hexagram 16. Which text do I read?
With no changing lines, read the judgment: "Yü indicates that, (in the state which it implies), feudal princes may be set up, and the hosts put in motion, with advantage." With changing lines, read the lines that changed. When several change at once, Zhu Xi's rules decide which text leads, and the casting page marks it for you.
What are the nuclear, opposite and inverted hexagrams of Yu?
The nuclear hexagram is 39. Jian (Obstruction). The opposite is 9. Xiao Chu (Small Store). The inverted hexagram is 15. Qian (Modesty).