Hill discounts column failure possibility
"I have listened and read endless theories about why, or how, he could have crashed on such a 'simple' corner like Tamburello," the Briton, world champion in 1996, wrote in the Times newspaper on Tuesday.
"No one other than Ayrton Senna and me know what it was like to drive that car, through that corner, in that race, on that day, on cold tires.
"Ultimately we will never know what Ayrton was thinking, or what really happened. I am convinced that he made a mistake, but many people will never believe he could."
Hill said the three-time world champion, whose death reverberated around the world and will be commemorated this weekend when Imola hosts what could be the last San Marino Grand Prix, was a great driver who pushed to the limit and beyond.
The cause of Senna's accident remains open to conjecture and an Italian court last month decided to reopen a manslaughter trial.
Team boss Frank Williams, technical director Patrick Head and former designer Adrian Newey, now with McLaren, face a new hearing after being cleared of manslaughter charges at a trial in Bologna in 1997.
There has been considerable speculation over the years as to whether the modified steering column on Senna's Williams had snapped, causing him to drive helplessly into a concrete wall.
Hill rejected the suggestion, saying the car had power-steering but he had driven the whole race with his turned off as a precaution after Senna's crash.
"In fact, the column could easily withstand the considerably increased loading for the whole race distance," he said.
"It is inconceivable to me that Ayrton's column could have broken with the power steering working normally, which I believe it was from the data subsequently retrieved from his car."
Hill also considered whether the race, won by Germany's future world champion Michael Schumacher in a Benetton, should have been canceled.
"I thought for a long time that the blame lay at the feet of those who make the rules," he wrote. "But now I see it as it is. It is sport. It is entertainment.
"You don't have to do it. Ayrton did not have to do it. He had a choice on that Sunday and, incredibly sadly, he made the wrong one."