Being uninformed about lube
First of all, do use lubricant when using a sex toy. If you need it during sex with a partner then you likely need it when using a toy, too. Being properly lubricated is important for preventing vaginal tears. Plus, it just makes sex a whole lot more fun. That being said, you might not be free to use whatever lube you have on hand with your preferred toy. Silicone lubricant cannot be used on silicone toys as it can deteriorate their surface. Silicone toys are to be used with water- or oil-based lubes.