Aikido is practiced with cooperative training instead of competitive training. An example of competitive training is sparring in boxing or a Judo match. In Aikido, one student executes the technique (nage 投) and that student's partner receives the technique (uke 受), then the roles are reversed. It is through this training that there are no winners or losers. There is only a goal of continuous self-improvement.
Cooperative training is necessary in Aikido because competitive training will lead to injuries due to the nature of the techniques or the techniques will have to be limited or modified to ensure the safety of the students. A good partner will provide physical feedback but will not resist or counter the technique. This method of "learn by doing" is important because there are many lessons that are easier to learn with experience than it is to learn by verbal instruction.
We practice within our partner's skill level while helping to expand their skill level. It is not uncommon to think you know everything there is to know about a topic, then to realize that there is much more to learn about it. It is also not uncommon to think you don't have the skill to do something when you actually do. A good student is always looking for more to learn about even the most fundamental topics.
Practice receiving a technique (ukemi 受身) is important to Aikido training. It is through this practice that students improve sensitivity and flexibility in movement as well as improving balance and development of core muscles. An hour of Aikido training is not 30 minutes of training and 30 minutes of waiting for your chance to train; instead it is a full hour of training.