So, Lone Spelunker is, in its own rudimentary way, a "cave exploration simulator". It's got a lot of the trappings you'd want for such a thing.
But, as I pointed out in earlier articles on storytelling and inventory management, a raw, realistic simulation may not be all that fun. If you're making a game, you're going to want to make some concessions to fun, in all likelihood.
Of course, Lone Spelunker is no different. There are places in the game's mechanics where I've bent the rules of realism and logic a bit to make gameplay more interesting. One such place is in the climbing mechanic. While you can grip the walls at any old location, you can only hammer pitons into places where there is a blank, unadorned stone wall. You cannot hammer pitons into empty air, nor can you hammer them into flowstone or other compelling cave features (because a good spelunker doesn't destroy such items!).
Now, technically, if it's stone you can grip, then you ought to be allowed to hammer a piton there. But when you can do that - essentially hammer pitons wherever you are - there's really very little challenge or danger to climbing. You don't have to spend nearly as much effort figuring out how to get up to that chimney leading out of the ceiling of the chamber, because you can just casually climb along the ceiling without even worrying about it.
After many playthroughs, I think I've got about the right mixture of flowstone, open air, and hammer-able stone to make climbing challenging but not impossible, realistic-feeling but not a gimme.
I do worry a bit that it destroys immersion. At some point, the player is going to think to him or herself: "I wish I could hammer here! Wait a minute, why can't I hammer here? If this were a real cave, I probably could hammer here..." But let's face it - if the game isn't fun, they're not going to stick around long enough to care. I'd rather have the game be fun and omit a few details than be accurate down to the carabiner and be exceedingly dull. It's a balancing act that every game designer must perform, and hopefully, I'm hitting the right balance with Lone Spelunker.