You watch TV for a bunch of hours and there's a constant hum of energy which is mostly just regurgitating the same information over and over again in different ways but there is a little kernel of new information coming out in dribs and drabs. And at the end of X hours it feels like those hours were spent productively because you have been exposed to new information along the way. Typically though you'd be better off just reading a summary later.
In an office environment when you work, say, 12 hours a day you'll find that you do productive work all throughout that period, even in the parts after "normal" hours. And that suckers you into thinking that the whole stretch was valuable, even though typically there are lots of periods of downtime and reduced productivity in those 12 hours and usually you'd be better off just working 8 hours or less and having better time management. Similarly, when you happen to overhear co-workers talking about something important and you go join the discussion and it turns out to be very fruitful you have that same post hoc rationalization that how things happened is the best and/or only possible way for productive work to happen.