Common mistakes that hinder progress in fitness routines include inconsistency, setting unrealistic goals, and neglecting proper nutrition. Many individuals often fail to track their progress accurately, which can lead to frustration and demotivation. Additionally, skipping warm-ups and cool-downs can result in injuries, further stalling progress. It's also crucial to avoid the "all or nothing" mindset, which can lead to emotional setbacks. By focusing on gradual changes and being flexible, individuals can create sustainable habits that yield long-term results.