Kata Geiko (Forms Practice)
If my partner is always helping me, how do I get better?
Like many other traditional Japanese martial arts, aikido is done through the format of forms practice. The roles are decided and each person takes turns. As a method of transmission, forms practice has a long history and is how many practitioners achieved mastery. The famous swordsman Miyamoto Musashi developed his curriculum to consist of only five forms. We can infer that there is much to learn from such a short "textbook".
Encounters with the Self During Repetition
From the very beginning, an aikido student is working with their own ambition, some goal that they are trying to execute in every movement, every technique. It is unlikely that even the most helpful partner will move exactly as you are imagining. So you will always have the opportunity to face the question, "What is really happening? Why does it not go exactly like I want it to?" Because there is no competition in aikido, the goal is not simply to make the other person fall down. Your partners are already helping you do that. And you may succeed at the cost of your posture, composure, etc. The goal, then, is to pursue, without being consumed by, the "how" one is doing a technique, and even more deeply, "how I am" while I am doing a technique.
The degree of cooperation by partners needed by an individual is something that gradually decreases. At the same time, the mental reliance (or insecurity) on set patterns decreases. The above are ideals and it's up to the individual on how things develop internally.