It’s not easy, it takes time and effort, but it can be overcome. Mindfulness, setting periodic alarm reminders (at first frequently and then less so) to sit up straight and breathe deeply, meditation, all help a lot. The problem is that it can take a while to start to see results, and people often give up. They’ll come back to it when they pull something or herniate a disc, but until then posture and breathing are not a priority.

You can definitely do it though, it just takes some initial inconvenience and effort. The payoff is not insignificant though, including positive impacts on productivity!