Gains goblins. Those things in your life that rob you of what otherwise would be your hard-earned gains on strength, muscle size, endurance or whatever other thing you want to develop by training.
It can be anything: a person (like that gym bro that maybe distracts you more than it's good for you), a medical condition, a commitment, or what is usually most common (and be honest here, because for most people it is one in this category), a bad habit of yours, amongst others.
Feel free to share.
My job. Working a blue collar job where you have to walk 15-20k steps a day is good I suppose for burning calories, but at the end of the day it's tough to add any sort of cardio or muscle building before or after the day. I try biking to and from work but then I'm really zapped and spend my evenings just lying around barely able to cook dinner. I have some light weights which I do sitting which is decent.