There is something that we all do, every day of our lives.
In our greatest days, we do not do it as frequently.
In our darkest hours, it is all we can do.
Only sometimes do we achieve what we wish.
So... I do it every day, I don't do it when the day is great, and I can't stop doing it when it's dark.
Alright. So, first off, we have to assume that whatever it is we're doing is occurring inside a vacuum-cleaner. That's the only way to ensure that total science is taking place. Science with lots of dust and crumbs.
Now. In order for a day to be great, the day needs to be fat. Like physically obese. It ate to many ice cream sundaes and now the day needs to get around on a fat-person scooter to buy even more ice cream sundaes from the sundae-store. Oh! That must also mean that the day is a Sunday. So that narrows our results down from seven possible outcomes. Or eight, if you believe all that stuff that Dave preaches in his dumpsterhome in the other alley.
We do it when the day is fat.
When it's dark, that could either mean that it's nighttime, or I'm in a windowless room, or Robert's blocking out the sun again. I'm assuming the second. So, if I'm in a windowless room, then I was probably lured in there by either a handbell choir or several hatfuls of Swedish Fish. In either scenario, I'd already be giddy as a spacedog in a bubbledream, so I might not notice the imminent dangers present in the darkened room. Like stones or treeple. I'd also probably fall down a flight of stairs.
SO THEN. That's the answer to your riddles. What is it that we do? We fall down several flights of stairs. All day, every day.
Does this mean you can tell me how to not fall down stairs? Or... wait!