The old saying goes, "practice makes perfect", but that's not necessarily true. Usually practice just makes us better at whatever we continue to work on. So the reality is that practice makes permanent. And if you're practicing bad habits, then those habits will soon become ingrained.
Approaching practice with a positive mindset can really go a long way in making practice productive. Set goals, measure progress and shut down those negative thoughts. Speak to yourself the way you'd speak to a friend.