There are a lot of illusions in ballroom dancing. That's why you can't watch ballroom dancers and try to imitate them. These illusions are created by the partnership, isolating movements of different parts of the body, shape, timing, size of steps, rise and fall, dance positions, head positions, arm positions, body lines, etc. What you think you are seeing and how it actually is performed is usually very different. At first when you know how it is done it seems illogical but after you study the action further it does make sense.
Rule number "ONE" in learning ballroom dancing is: "Know what you are doing!". That means learn exactly how that movement is performed. Every thing we do in ballroom dancing has a reason. Nothing is done arbitrarily. Most movements are done in the same manner you would do them in every day life. However, because we are a four legged animal when we partnership dance, some things are a little different.
Everything we do in ballroom dancing relates to partnership, balance, control, power, speed, lines, characteristic of the dance, etc. Generally, if a man does not have a reason for doing something, he won't do it. If you don't know why you are supposed to do something, ask and find out. It will make you a much better dancer.
A simple example of a ballroom illusion is "speed". You watch an experienced couple fly around the room dancing a waltz. So you try to dance at the same speed but find out that you can't stay with the music. You are way too fast. Then you see an older couple dancing very slowly to the same song. As you watch you realize that both couples are dancing to the music. How is this possible? It is quite simple. The experienced couples are taking much longer steps so they have to cover more distance in a beat of music resulting in faster body movements. The older couples are taking smaller steps so their body movements are slower. As you watch, you notice that each couples weight changes are at the same time and with the music.
Another example is a lady's underarm turn. The leader always determines the speed of the turn in one manner or another. In a two step underarm turn, the leaders weight changes which is felt through the connection and tells her how fast to turn. In a powered turn, the leaders connection powers the turn. In order for this to work, the lady must not turn herself. The lady actually pushes against the direction of rotation to add control and power to the turn. If the lady turns herself in the direction for the rotation, she will pull away from the leaders connection and loose the power and timing of the turn. A leader can lead the same waltz turn as 1,2,&,3 or 1,&,2,3 by the timing of his connection (unknown ahead of time by the lady). This is true lead and follow. You can't tell by watching these turns how they are being performed.
Ballroom dancing is based on the physics and geometry of a four legged animal. This four legged animal is a little unusual since the front half and back half are facing each other. The most important thing in ballroom dancing is the quality of movement not the number of patterns you can stumble through. If you want to be a good ballroom dancer take the time to find out how these movements are best achieved. Instructors have been working for decades trying to find the best possible ways for this strange four legged animal to move to the music.