From: Groningen, NL
To build an asset you need to work on it a certain number of turns, spending a certain amount of resources each turn.
Now you cannot work harder on it than the requirements, but when even one worker has a bad day, failing 1% of the effort, it immediately increases the production time by one turn. For material resources like production and metal, having enough in stock will guarantee that those will not be the bottleneck, but with the workers you don't always have the means to guarantee their productivity.
I find that a bit quirky. But I know that Shadow Empire is a game for masochists :-)
Also, I have now become hesitant to start producing a new asset before the old one is completely finished, because I see often that when there is a bottleneck caused by the new building, the older one in the queue, which needed only 1% more to finish, didn't take the resources first to finish and deliver its benefits, but somehow the new building in the queue took everything available.
So trying to build as fast as possible will often be counterproductive when the smallest setback happens during the turn processing.