Doing way too much exercise can 'lock' your body preventing fat loss or muscle gain.
Because of not having proper rest your body won't have time to recover.
Performing exercises without a plan can result in delayed results.
Not having a proper warm-up routine can make you prone to injuries.
Doing cardio before weight training can exhaust you, hence limiting your performance.
Hydrating during a workout is crucial to prevent exhaustion.
Not knowing the proper way to perform an exercise can lead to injuries.
Lifting weight more than you can handle can lead to severe injuries.
Not having proper clothes can restrict your movement during exercise.
Without consistent training people can not have good results.