Every kind of intrusive procedures come with a certain degree of pain. Liposuction is really not as simple a procedure as you imagine. It's considered a major surgery. It does involve a thin tube passing through under your skin, in your lipid layer, to suck out the fats. In that process, you run the risk of causing excessive vascular damage, which could cause excessive blood loss. This is also why most people who'd done liposuction takes a while more all the bruising to go down.
In addition, because it's an intrusive procedure, you are at risk for infection, on top of the stresses on your body during the general anaesthesia. You'll also need to wear a constrictive garment for some time to help bring down the bruising, inflammation process, and to help tighten the excess skin that's left behind after the fats is removed.
Some people bounce right back post-surgery. Some people experience a lot of pain and complications. It depends on how expert your surgeon is at performing this procedure. Remember that the surgeon has no way of gauging where the tube goes, as it's more of less a blind procedure once the tube is in your body. As such, punctures are potential risk factors as well.
If you're interested in undergoing liposuction, after you've tried hard in vain to lose the stubborn fats, do your homework thoroughly to ensure that you've chosen a well-qualified and experienced surgeon. Ensure a comprehensive medical and surgical history taking, blood works, take a tour around the hospital ward where you'd be staying, your room, etc. NEVER decide on plastic surgery on a whim. ALWAYS think think think and rethink, and clarify every single queries and doubts that you've got about the procedure.
Your surgeon should be able to answer ALL your questions without seeming on guard. And he/ she should be able to provide ALL the necessary information regarding this procedure, before and after care, what you need to do to ensure long-term maintenance, as well as a comprehensive pre-op consultation to ensure that you're not going for the procedure without having tried other means to lose weight more safely.