The logical outcome of perpetual cloud cover is a world that is exceedingly wet. This would have a number of effects, but I'll just list 3 as I'm guessing this is not exactly what you meant.
1. Disease Spreads more Rapidly / Medicine Advances Faster (When Possible)
The very wet environment would help transmit a huge number of pathogens. As a result, people are very motivated to solve medical questions. When advances are possible, those advances occur quickly.
But note that not all advances are always possible. Without the microscope, for example, microbiology would not be an available field. Of course the microscope would probably take longer to invent since there was no need at all for anyone to work on improving lenses for Telescopes except for basic navigation or warfare.
2. Cities Form More Slowly
Due to the wet climate breeding parasites people learn fairly early on that living in close quarters with other people is much less advantageous. In fact, it seems like every large community has a massive disease outbreak every year or two that you might better avoid by living further apart and interacting less.
The only large/successful cities would be those that evolved following fairly strict practices which - as they would discover many hundreds or thousands of years later - happen to be more hygienic.
3. Shipbuilding & Exploration Occurs Faster
Being very wet, everyone needs ships to go any notable distance. Rivers everywhere. So ship building takes a big leap forward. Exploration of new lands occurs much faster as a result of both increased numbers of ships and faster improvements in ship building techniques.
As for how people feel when they do get above the clouds...
In awe, I would suspect. We were pretty surprised when we got into space and found out it wasn't made of ether, but as we'd been staring up there for a long time we had plenty of evidence to help us get over it. Your people would have no idea about what to expect at all.
Send up a plane in the day: The sky is blue and there is a big yellow thing in the sky!
Send up a plane at night: No, the sky is black now and there are stars everywhere. And a moon! Only this civilization literally no words for "stars" or "moon", so they have to describe them in other ways.
Send up a plane at twilight: No, the sky is reddish! I can see the moon, but no stars???
The huge conflict in the day/night cycle and the discovery of all celestial bodies would be significant drivers to motivate people to build more planes and send them up day and night. Space exploration would probably happen at the first opportunity.
Oh, and surely all sorts of religious heck would break loose.