Who hasn’t been persuaded by an 18-200mm lens for under $400 or an 18-50 IS for only $100. Why would I spend $1000+ for a fixed lens without image stabilization when I can have a full zoom for ¼ the price?
This is an issue I cannot stress enough. You must be diligent about backing up your photos, videos, and other important data, especially if you are using that information professionally.
ISO can be a very important tool in digital photography. It allows you to capture great images in low light when used properly, yet without a firm grasp on the limitations of your equipment, it can very easily ruin your photos. Most digital cameras allow for manual over-ride of auto-ISO. Learning to master when and how to use ISO will be an important step to improving your photographs.