If Yì has appeared in your reading, the book is naming a season of augmentation. Wind and thunder reinforce each other; their combined force is greater than either alone. The hexagram appears when resources — material, emotional, social, creative — are flowing toward the reader, and the configuration is favourable for putting them to use.
Classical commentary reads this hexagram as the direct counterpart to Sǔn (Decrease). Where Sǔn is the careful reduction that simplifies, Yì is the generous flow that augments. Both are part of the same circulation. The book treats wealth — in any of its forms — as something that becomes destructive when it stops moving and generative when it continues to.
What the book counsels is the immediate, generous use of what arrives. The two clearances — fit to have a place to go, fit to cross the great river — are unusually broad. Major moves are favoured. The image's instruction is psychological: see good and move toward it, see faults in oneself and correct them. The increase is meant to fuel both kinds of motion.
Yì's failure mode is the hoarding of the inflow. The book treats this as one of the gentle but reliable ways the season turns against the reader. Resources held in place stop being augmentation and start being weight. The hexagram appears when something good is coming in. The work is to let it pass through the hands while it is doing so, in directions that the next season will validate.