Yes, it absolutely is hard to understand. Just look at how many threads there are, on this forum and elsewhere, complaining about this very point.But, so long as you know one thing: Building the forge will take workers from elsewhere, where is the surprise? Is 'This thing provides more desirable jobs than that thing' thus creating a trade-off so very hard to understand?
In this case, I was many hours into a game, and had just noticed it was possible to buy exotic materials on the market to upgrade the forge. It wasn't intuitively obvious that should be possible to buy exotic materials, given that I didn't have the technologies to extract them. It wasn't obvious that an upgraded forge would require more workers. The UI depends on mousing over tiny icons, hard to distinguish, and not all of which even have mouse-over text.
So I tried something I didn't know I could do, didn't notice the obscured indirect costs, and didn't realize that those indirect costs were huge.
Bad communication, in itself, is enough to make it a bad system. For one thing, if you're designing a game, you have to design it around how it will be communicated.I'm not seeing this as a bad system, but rather its a bad communication of a system.
As it stands, this has become a game that actively punishes the player for experimenting. Most of the advice I'm seeing for how to play the game now, emphasizes very conservative play: avoid building things or upgrading things; if you're not sure what something is you shouldn't build it; concentrate on the basics that you get at the very beginning; don't expand. The feeling I get playing now is a constant nagging worry that I'll break something if I mis-click. It's just not fun.