Here’s a couple of scenarios – which of these is more likely to work under stress?
Evil guy surprises you and you step 45 degrees to the outside of the attack into a strong position, grasp his wrist with a specific grip and execute your cool move on him.
Evil guy surprises you and you move offline however you can, put your hands between your face and his, close your hands on whatever they happen to come in contact with, and continue moving in whatever direction you happen to be going to try to push/drag him offbalance.
Under stress, people tend to lose fine motor control. As a basic example, think about trying to sign your name legibly while sparring with someone. Point is, you have to build your system out of gross motor skills instead of fine motor skills or it stands a greater chance of falling apart under stress.
Aikido is just such a beast. The basic response that we work on during every single class is, “step offline, put your hands up, and keep moving.” Gross motor skills. What is really cool and amazing is how much of the magic aiki stuff can be replicated with that simple a ruleset. Easily 85% of aikido is doable with pretty gross motions and pretty gross timing.
So, next time someone tells you “step at this particular angle,” or “grab this particular way” or “push here just so…” think about signing your name while sparring.