There's nothing similar, but "you're confused between porridge and gruel" comes closest.
Thats means that you are knowledgeable, but ignorant on the finer details that makes the case different. When you're troubleshooting something, it fits.
Similar ones would be:
"You're standing on the hose" (you're very close to finding the solution but you just can't)
"You're bridling the horse from behind" (You're looking at the problem the wrong way)
"The other way around it becomes a shoe" (same as above)
I believe this is Swedish ("ser inte skogen för alla träd").
An attempt at a alternative translation; "can't see the forest because of all the trees". Which means you're perceiving the wrong part of the situation, and thus missing out on the bigger picture.
I like how you said it's hard to translate to English, but English has the same saying. The saying must have a common ancestor between our two languages! (Or maybe one is the common ancestor...)
It indicates a gross mistake, the achievement of a much lower result than hoped for or, more rarely, purchasing something believing it to be of much higher value than it actually is.
This expression, among the most common used in Italian to indicate a mistake, has its origins in fishing , particularly sport fishing. If you lower the line into the sea until you reach the seabed and touch the bottom with the hook and the bait, it may happen that a crab bites instead of a fish . As soon as the crustacean is hooked, it immediately begins to struggle violently to free itself from the hook, giving the fisherman the impression that it has instead hooked a large prey.
Fishing for a crab with a rod is normally a source of disappointment for the fisherman, since it is a useless prey, which in some cases can even damage the line. The origin of the phrase was born from this disappointment, generated by the expectation of a large fish.