Why is my high poly 3D model laggy?

High poly 3D models are laggy primarily because their large polygon count increases computational load on your CPU, GPU, or RAM, slowing real-time rendering. More polygons mean more vertices and surfaces for hardware to process each frame—this strains resources, especially in tools like 3D editors or games where real-time display is key. To reduce lag temporarily, try using level of detail (LOD) models or hiding unneeded parts in your 3D software.