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.
I have probably more than one, but my silliest and, at the same time, most annoying one is an object: my wireless earbuds. I cannot put my phone one meter away without losing signal and my music cutting out. Not even carrying it in my pocket works, and at the end of my training session I have lost a ridiculous amount of time trying to get those things to work by turning them on and off again or resetting them. I would buy new ones, but alas, there's no money for that.
You can get pretty good Chinese iems for a price that's not all that expensive. They'll probably be wired but you won't have to fiddle with them so much.
Both my airbuds and phone are Chinese already and they are both malfunctioning terribly despite the fact that I have only had them for 2 years at most. I guess one day I'll just have to renew my electronics and compensate the expense with soups for dinner for a few weeks.