In Star Wars: Episode I - The Phantom Menace, the Jedi Council almost unanimously rejected the idea of Anakin Skywalker being trained as a Jedi, deeming him too old to be trained. Yoda also sensed fear in Anakin, which stemmed from being away from his mother, Shmi Skywalker.
However, despite all that, Qui-Gon Jinn was adamant about training Anakin and believed that Anakin was the "Chosen One." Everything Qui-Gon hoped for happened after his death when Obi-Wan Kenobi took Anakin as a Padawan. What all this led to is horrible, but this tragedy could have been avoided if Qui-Gon hadn't made one key mistake: Leaving Shmi behind on Tatooine.
Leaving Shmi was a huge mistake
Qui-Gon made a bet with Watto that if Anakin won the Boonta Eve Podrace, then he'd be freed. This left Shmi a slave on Tatooine, while Anakin raced to his freedom and agreed to go with Qui-Gon to Coruscant to be trained as his Padawan. While the idea of becoming a Jedi seemed appealing to Anakin, leaving Shmi behind was a huge blow to him, and he never got to return and free his mother as he promised.
The mistake was Qui-Gon's, as slavery was rampant in the galaxy, and taking Anakin to live the life of a Jedi while his mother remained a slave wasn't the best decision. He should've thought of a way to take Shmi with him or, at some point after taking Anakin, should've discussed freeing Shmi with Obi-Wan. Having his mother around could've helped Anakin deal with the changes he went through and spared him the trauma of separation.
Shmi was vital to Anakin's upbringing
Qui-Gon was a far more broad-minded thinker than anyone on the Jedi Council. While the Jedi Council feared attachments, Qui-Gon could've ensured that The Chosen One got to be with his mother whenever he wanted to. To put it simply, it makes no sense to have left the woman who gave birth to the Chosen One a slave. The idea of freeing Shmi before leaving the planet should've been something that Qui-Gon had thought over a great deal, and before leaving, it should've been Qui-Gon who promised that Shmi would see Anakin again.
Though Qui-Gon, Obi-Wan, and Padme didn't have the means to pay for Shmi's freedom, something should have been arranged. As Anakin's mother, Shmi was vital as she knew her son better than anyone. Anakin wasn't just any Force-sensitive child; he was the child with the highest midi-chlorian count ever seen.
As the Chosen One's mother, Shmi should've been a priority. Unfortunately, Qui-Gon dies very soon after Anakin leaves Tatooine. In the years following his death, no one in the Council even considers freeing Shmi and allowing Anakin to meet her. The council continued its archaic practice of rejecting attachments. By keeping Anakin from meeting his mother, they pushed him further into the darkness. Anakin never got the opportunity to visit Tatooine and see Shmi, and by the time he could do it, it was too late.
The Jedi Council failed Anakin and Shmi
As the keepers of peace in the galaxy, the Jedi showed how useless they were by doing nothing for Shmi. With hundreds of Jedi alive before Order 66, nothing was done about the issue of slavery. It was unfair to Anakin that, as the Chosen One, he was expected to bring balance to the Force, but there was no balance in his life. His mother's absence weighed on him until her death, and after her death, he was filled with rage at his failure to do anything for her. Ultimately, the blame for all this falls on the Jedi Council for failing to pinpoint the issue with Anakin.
Qui-Gon could be deemed wrong for taking young Anakin away from his mother and not ensuring she was freed, but he had very little time. The Jedi had years to consider this decision, but their lack of concern and inaction led to disaster for Anakin and Shmi. They never allowed Anakin to check in on his mother and ensure she was safe. Anakin had to hide to find Shmi as he had promised to return, and it's not something we can blame him for doing. Though it was too late and became the event that triggered Anakin's descent to the dark side, it might be Anakin's most humane and Jedi-like moment to return home and fulfill his promise to someone he loved.
Unfortunately, the Jedi never took this issue as seriously as he did. Anakin's fall might've been avoided completely, and Qui-Gon Jinn's mistake of leaving Shmi behind could have been corrected.
Star Wars: Episode I - The Phantom Menace is streaming on Disney+.