1-Giving up in the first week because you don't see results. Muscles growth requires continued exercise.
2-Giving more importance to quantity than to quality.
3-Not giving importance to nutrition.
5-Not eating enough calories.
6-Not sleeping enough.
7-Not drinking enough water.
8-Not being focus.
9-Doing long breaks between exercises.
10-Not establishing goals.
11-Doing always the same workout.
12-Doing the regular sit-ups.
13-Not eating enough carbohydrates.
14-Not ingesting enough proteins.
15-Exercising the same muscles everyday.