There are several models we might consider.
*Your main problem is your enemies.
*Your source of obstacles is your rivals.
*Your problem is a system or set of circumstances that is rigged against you.
*Your problem is your own self or behavior.
*It is something else? Random events? Sheer luck or the lack of it?
Any of these frameworks might be correct for a given problem. I don't think I have enemies to speak of, and if I do I don't think they are doing much harm to me. My rivals aren't hurting me. I might envy Christopher Maurer and Andrew Anderson their superior knowledge of Lorca, but nothing they do holds me back in any way, and in fact it furthers my own ends.
The system is rigged in my favor so it's not that.
So in my case the majority of barriers to productivity are self-generated. And, frankly, I am productive so even here these barriers cannot be all that frightening. Yet I find that they are... I'm publishing my book later than I thought it would come out, for example.