I think when I say I don't have free will, I don't think it automatically means I am scapegoating criminal intent, an usual obstruction to this question. For a while, let's dissociate the morality question and answer this simple question: if I were born somewhere else, the son of another set of parents, would I be able to think about the thoughts I currently have? And therefore, consequently, the actions that must step from both the conscious, the tip of the thought iceberg, and the rest, the huge part that's beyond my reach? No, right! It's really that.
Can I not will something? Yes, I can, but that isn't something that's ex nihilo. It's still the same biological circuit underneath, or flitting thoughts, both conscious and not, carroming into each other, that's once again constrained by genes and environmental factors (including prenatal up to this point in time). There's nothing we can do to shake ourselves out of this and behave like someone who isn't constrained this way.
I think it's the byproduct of the illusion of delay and path. It's like water that starts without letting us know, in the shrouded and misty mountains of the unconscious. But when it flows into the lower (in this metaphor) terrain, where it registers as conscious thought and "only then" sometimes as speech or action, do we conclude that it's in our conscious will? But even otherwise, it bounces off the walls in the conscious cave as that inner speech—that is, speech that's mute but of our own volition, again, all part of that singular illusion.
In the early 1980s, neuroscientist Benjamin Libet conducted a series of experiments to explore the relationship between conscious intention, neural activity, and voluntary actions. Participants were asked to perform a simple voluntary motor action (e.g., pressing a button) while watching a clock. They were to note the position of the clock hand when they first felt the intention to move. Meanwhile, Libet recorded their brain activity using electroencephalography (EEG). Libet found that a specific pattern of brain activity, known as the readiness potential, preceded the conscious intention to act by several hundred milliseconds. This suggested that the brain was preparing for action before participants were consciously aware of the intention to act.
If only we could invent that elixir that bypasses the conscious and goes into language and action, we'd know for sure that this is indeed possible, not just in sleep or when inebriated but with experimental control. And then we'll know that, unless the unconscious part that's generating these is part random and part initiated by feedback from bouncing thoughts, but controlled inherently by the biological and environmental past, and therefore not the "will power" we are so proud of, but only a misunderstood reality of a complex neural circuit, when it's still too difficult to look at the cogs and wheels under the hood.