garbage in, garbage out idiom mainly US saying
垃圾进，垃圾出（意为用劣质的材料生产出的产品也必然是劣质的）
something you say that means that something produced from materials of low quality will also be of low quality
The meals are pretty poor but then they never use fresh ingredients - garbage in, garbage out. 这饭真难吃，因为他们从来不用新鲜材料——也难怪，垃圾进，垃圾出。