1: You're not even there in spirit. You might show up and execute all sets and reps, but you're doing it without any attempt to improve since your last workout.
2: You choose your favorite muscle groups and then fail to do the ones you don't enjoy doing, usually by procrastinating them into Sunday. And then you go oh well let's start fresh on Monday. But on Monday you don't start with the muscle groups you neglected, but with your favorite ones again, resulting in complete lack of stimulation of your weak spots for weeks.
3: You go work out at the happy hour time when everyone else is working out. You do this subconsciously so you have an excuse to avoid the compound moves since everyone is doing them, and the racks where you perform those compound moves are busy.
4: You don't time yourself between sets, so they end up being 5-minutes long and you're not a power lifter trying to max out on singles. Then at 45-minutes you've got to go, you've done 10 sets….
5: You allow yourself to work out only when you're in the mood for it, but sadly you're not in the mood that often.
6: You stop when it hurts - as in when your muscles are actually starting to get challenged.
7: You forget to prioritize. You get wasted on cardio when you're trying to pack some meat on those wheels.
8: You’re lifting too light. How do you know it's too light? You're not worried that if you lose focus you'll get hurt. If you're not getting hurt when you lose focus it's just not heavy.