One of the big changes in D&D over the years has been the addition of skills. Originally, there were only a few skills: roll a d6 for finding a secret door, for example. Then our friend the Thief was introduced with his many skills. Now we could roll to see how well a thief hides or how silently the he moves.
Of course, there were people asking for spot and listen skills so they can try to find hidden things and listen for those trying to be silent. But that's not how older D&D works. If you're not a thief, you have no skill in hiding and you have no skill in moving silently and the DM and players just have to use common sense to find out if someone can see an unskilled character trying to hide. And characters can't get skilled in trying to spot hidden characters or listen for those silently moving. Everyone can see and listen the same. The real skill is in the hiding and moving so you can't be seen and heard.
That seems the basis for older D&D. Only the remarkable is made into a skill. Moving silently is really hard to do well. So is hiding in shadows or climbing sheer surfaces or disabling a trap. Older D&D gives percentages there but for everything unremarkable, there's no roll. You're an adventurer - of course you can do it! Roll a die if you think there's a chance of failure but it's not remarkable so we're not going to give a rule for it.
That's what I love about old school. I don't want rules for the unremarkable. I only want rules for the remarkable stuff. Let my game be made from the stuff of legends!