One of the most common questions Batman is asked is why he allowed an eight year old boy to become his vigilante partner in the city with the highest crime rate in the world.
Usually it has been the other Justice League heroes who have asked him this question, and Batman, being the good hero and friend that he is, has always ignored them or thrown his notorious bat-glare at them, scaring them to death.
However, there were occasions when Batman was forced to answer their question and each time the answer was always the same.
Robin needed to help bring the men who murdered his family to justice.
So he wouldn't turn like him.
This was certainly true but it was not the complete truth.
What he did not tell the others was that he would never want Dick to become Robin.
As if Bruce wanted to introduce his adopted son into his violent and cruel world. Bruce just wanted Dick to spend the rest of his days as a normal child without worrying about knowing how to dismantle a bomb or how to throw a roundhouse kick with just enough strength to knock out a criminal.
Bruce just wanted his son to live a normal life without seeing things that would leave scars (both physical and mental) on his body and soul, without him waking up in the night because of a nightmare about the Joker or Two Face.
But no. Dick was the most stubborn child (later man) he ever met, likely even more so than he was.
What Batman left out every time in his response was the fact that Dick had given him an ultimatum: either Bruce would train him personally and they would patrol Gotham together as a real team or Dick would go out alone on the night streets and surely die within a very short time.
So Bruce had had to surrender and train Dick, much to his son's enthusiasm and his (and Alfred's) dismay.
Moreover, Dick's damn puppy eyes had not helped Bruce at all.
When Bruce first started training Dick he had gone very hard and heavy on his son and the training was always harder and more intense than Bruce himself had wanted in the hope that Dick would change his mind.
What a vain and illusory hope.
Of course Dick Grayson was not supposed to be like a normal child.
He wasn't.
Dick learned everything Bruce taught him faster than the billionaire expected. The more Bruce threw tests at him, the more Dick was able to pass them with an ease that was honestly frightening even for Bruce.
There wasn't a damn test Dick didn't pass.
Bruce reluctantly admitted to himself that Dick was a natural and that one day not far off Richard would become better than him in every way.
And with a pride so strong that only a parent can feel Bruce witnessed this. Nightwing was Batman's greatest achievement, and the Dark Knight was proud to say that the student had surpassed the teacher, just as he had expected from the first time he began training him.
So yes: what Bruce told others was true but he always left out the second reason.
He could not admit that an eight year old child had actually blackmailed and coerced him, The Batman, the notorious Dark Knight of Gotham who strikes terror in the hearts of criminals and superheroes with divine and superhuman powers, into training him.
His reputation depended on it!
So yes, here is the real reason Bruce trained Dick.
And Bruce would have personally made sure it stayed between him, Dick and Alfred.
Spoiler: it didn't.