Sticking, joining, adhering are integral aspects of T'ai Chi.
On the physical level, we practised a simple partner work. Pair up with a partner. Place your hand lightly on the back of their opposite hand. Don't cling to them as if they are a meathook. The touch should be light and sensitive. Close your eyes. Your partner then moves his hand around and you follow, maintaining a light touch. Listen with all your senses. You then swap to the other hand and after that change roles, in which you become the leader. There is to be no talking during this exercise.
This exerise builds up a familiarity with touch and develops listening and sensitivity. As with pushing hands you need to practise with lots of different people to appreciate the differing qualities of contact. This approach is then carried over into your pushing hands and also your form. Even though the form is a solo practise, you can listen to what is around you, imagine moving with a partner, be light, sensitive and spirited.
Then there is joining and sticking to the energy of another person. The process begins before the touch. You enter and join with their energy immediately. There must be no delay, no conscious deliberation. You become a part of them.
Sticking is active, not passive. Sticking becomes part of yielding. This is a deep topic and I will come back to some of my experiences in a future post.