There are many systems at work in the brain at once: the emotional system, the habit system, the reward system, the risk-assessment system, the social judgment system. They compete with one another, pull against one another, and ultimately produce a behavioral outcome.
Consciousness is not always the starting point of decisions, but it often organizes and explains the result, and sometimes it can also correct it.
So the clear, unified, absolutely autonomous intention we think we have mostly does not exist. The intentions we experience are often more like a simplified conclusion, compressed from complex brain processes and handed up to the level of consciousness.
Many behavioral patterns do not exist because some individual “figured things out,” but because over long evolution, certain tendencies were more likely to survive and leave offspring, so they were retained. This process does not require a prior, lucid, planning subject. It is more like the environment sorting for you after a huge amount of trial and error.
From this perspective, humans really can be understood as always “moving randomly.” It’s just that these “random movements” are not completely average randomness, but “biased randomness” constrained by bodily structure, neural systems, hormonal mechanisms, the social environment, and evolutionary history. What survives in the end is often not what is most correct, but what is most able to survive.
So why do we still feel like we are making decisions?
Because the very feeling that “I am deciding” may itself be a useful adaptation.
A creature with no self-narrative ability at all would have a hard time steadily planning, reviewing, making commitments, cooperating, and would also have a hard time taking responsibility in society or maintaining consistency of identity.
By contrast, if the brain can organize behavior into “I did this,” “I chose this,” “I’ll change next time,” then that creature actually has an advantage in group life.
So the “sense of self-will” is not necessarily there to accurately describe real causality; it is more like a management tool. It helps us string scattered behaviors together and form a continuous personal story. That story is not necessarily completely true, but it is often useful.