One of the most iconic moments in the entirety of Star Wars happened in The Empire Strikes Back when Darth Vader froze Han Solo in carbonite. While Chewbacca and Leia were worried about their friend, Boba Fett was more concerned about losing his bounty. The only person in the room who knew it would work was Darth Vader because he tested the procedure on himself during The Clone Wars.
Carbon-freezing was an important process in Star Wars. A liquid substance, carbonite, could be changed into a solid by flash freezing it. While it was most frequently used to store and protect various goods for transport, it played an even more essential role in the early days of space travel. Before the invention of lightspeed travel, people making their way through space were frozen in carbonite to survive the trip.
By the time Darth Vader dumped Han Solo in a carbon-freezing chamber in Cloud City, it had been a long time since people traveled that way. But Vader was planning a trap for his son and wanted to test it on his son's friend first. Retrospectively, that scene really highlights how big a jerk Vader truly was. The problem was that modern carbon-freezing chambers were not designed to safely process people anymore. However, Vader knew differently from experience.
In Season 3, Episode 18 of The Clone Wars, a Jedi Cruiser commanded by Captain Tarkin was bringing Jedi Master Even Piell back to Coruscant. They had obtained priceless information about secret hyperspace routes. Naturally, the Separatists attacked and captured them, taking them to a prison called The Citadel that had been specifically designed to keep Jedi both in and out.
Anakin Skywalker and Obi-Wan Kenobi headed up a rescue mission that included Commander Cody, Captain Rex, Echo and Fives. Despite being ordered to stay behind, Ahsoka Tano snuck onto the mission as well. The first problem was getting past the bio scanners. Anakin came up with the idea of freezing the team in carbonite to mask their biosignatures and using captured Separatist Battle Droids to fly their ship to the prison.
While he didn't say anything at the time in The Empire Strikes Back, Vader had already successfully tested the process on several relatively willing volunteers years earlier. The plan to infiltrate the prison worked, and everyone survived the carbon-freezing process during the Clone Wars. That being said, Vader also wasn't particularly concerned about Solo's survival, either. If he died, he died. Though Vader would have then had to cover Boba Fett's losses.
To those watching the movie, it seemed like the Sith Lord was coming up with an ad hoc plan on the fly. However, what fans learned from The Clone Wars was that Darth Vader had personally gone through the carbon-freezing process decades earlier and knew that his son would also survive the experience. He just didn't count on how hard Luke would fight him before springing his trap, the only flaw in an otherwise solid strategy.