I am not sure if this is exactly relevant to this discussion (and if it isn't, I am sure a mod can split it off into its own thread), but this discussion of skill checks and DCs and what is achievable (with difficulty or not) and has an actual consequence got me to thinking about when I don't know exactly what success looks like as the DM - and I thought of a situation that happened just yesterday (and not for the first time) and how I use the skills to shape what happens in both in regard to the action itself and the setting/narrative.
In yesterday's session, the party was investigating the the hulk of a wrecked ship set adrift, and as the majority of the party approached on a rowboat to climb aboard, the druid transformed into an octopus, first to scope out the area, and secondly if he could find a hole that he use to squeeze his octopus form through (since they can squeeze through very tiny holes, it made sense that there could be tiny breaches in the ship hull that were not immediately visible and were leading to the ship very slowly sinking). And yet, despite my copious notes, it was not as if I had the hull of ship detailed in terms of every possible hole and its size - but I also didn't want to shut down the player's ingenuity by simply saying "there are no holes."
So I started an (easy DC 10) perception check to notice the patterns of small bubbles on the hull, an investigation check to pick out and follow a particular trail of bubbles to a possible hole. This took a couple of rolls because I ruled the low rolls led to holes that were too small because he misjudged. (the consequence for failure being the continued time spent searching while the party was split and at this point could mean separated and deadly encounters (as it was the rest the party did have a combat encounter while the search was happening). For squeezing through the hole, I decided he finally found I required an Athletics check (DC 15), with a failure meaning while he could squeeze through, it'd leave him vulnerable on the other side as he was partially through.
Eventually (after avoiding some ghouls in the bilge), he was able to rejoin the party mid-battle on an upper deck of the ship.
I guess my point being, skills are about accomplishing things (obvi) but they can also help address unexpected things in the game and create new opportunities for fun/suspense.