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.
Yeah now that I think about it you're right. A better example may be overcrowded gyms. I used to go in the evenings and it would be so busy to the point of not being able to do certain exercises because they gym was closing. Glad I can work out at home right now.