By shear luck, Grant achieved victory at Fort Donelson. Admiral Footes's Navy Ironclads were spanked and sent drifting dead in the water northward back to Cairo Illinois. His ships took a beating from the Confederate battery on the river.
CSA officers Floyd and Pillow made a huge tactical blunder after Day 1 of fighting that had hammered the Union and drove them back from their lines.
In fact, Grant had a surrender letter penned that due to the gift from his West Point buddies, he never had to use
If the CSA had gone on to win at Donelson Grant would have never been. He would have been sent back to Missouri where he was selling firewood after being thrown out of the Army for being a drunk.
Now you know some facts about our Civil War.
Glad to help.