Eureka moments, is the subconscious assembling conclusions and deductions and presenting them to you. That the subconscious is engaged and busy, is fed with information to build stuff from and rewarded for its actions - thus repeats it, is all conscious choices, thus subject to free will. The horse does pull of a record and the rider barely had to steer, is not a indicator of wild horses.
One thing I've discovered and utilised from a relatively early age was synergising the difference in how my conscious and subconscious processes information. It's really just the usual advice of "when stuck, go for a walk" but in my experience it's a very useful tool when done mindfully.