Sticking Hands, from Wing Chun Kung Fu, is a very useful martial arts training exercise, and Tai Chi practitioners may notice that it's surprisingly similar to Tai Chi's popular Pushing Hands drill. But there are a few key differences...
In Sticking Hands, you just need to create a small opening to hit the other person. You don't need an extremely strong stance, because the weight of the body is generally enough to support a useful punch to a vulnerable spot on the opponent's body (such as eyes, nose, neck & solar plexus). If someone tries to teach you otherwise, they're usually just using better hand techniques and pretending that it's all about the stance.
But in Pushing Hands there's a lot more time to defend when someone tries to push. Your stance can sink back to absorb the energy over some distance. Not only must you touch them firmly, you must follow through until they take a big step back. In Pushing Hands it's not just a case of finding a gap, it's about finding a very strong route to move through that gap.
Pushing Hands, indeed, is more forgiving of momentary mistakes. There's more room for defence and in some way less room for attack. But this is only due to the rules of the game, and on the streets these rules don't exist. So maybe too much Pushing Hands gives you a false sense of confidence in defence? But when a strong punch on the nose can kill someone, perhaps your personal code of conduct should usually make use of Tai Chi Pushing Hands restrictions on attack?
Sticking Hands is like the cherry on top and maybe some pieces of fruit in the middle of the cake, while pushing hands is the bulky part of the cake that really fills your belly. What I mean is, Wing Chun's Sticking Hands is the tight, fine pinacle of sparring, suitable for when your back's against the wall; while Tai Chi's Pushing Hands is more dynamic & rangey, using more of the body to form a softer, more flexible front. But they're both so similar, so simple yet sophisticated, with so much in common, it makes good sense to bring them both together.
Anyone who's mastered Wing Chun & Sticking Hands can gain a lot from also practicing Tai Chi & Pushing Hands. I know this from personal experience. I first started Tai Chi and Pushing Hands classes at a time when I'd just about mastered Wing Chun and Sticking Hands. I'd reached a par with my world-famous Wing Chun teachers so I thought Pushing Hands would come very easy to me. It did, but only as far as being average amoung the senior students. Meanwhile, I could see the senior Tai Chi students struggling with rapid striking & blocking, such things being integral to Wing Chun & Sticking Hands which I would have taken advantage of if it were a Wing Chun class.
It's like sweet & sour. 2 different styles of food, but most good chefs want to master them both in order to serve a full 3-course western meal. From a martial artist's point of view, Sticking Hands is slightly more about boxing (striking), while Pushing Hands is slightly more about wrestling (grappling), even though they're not a whole lot different in terms of basic sticking and pushing.
By the way Wing Chun classes typically emphasise the striking part of Sticking Hands, and the way Tai Chi's Pushing Hands involves a little bit of grappling, you could say these 2 exercises are like chalk and cheese, but they're still so similar in principle, in fact, they're almost identical.