Every solution will cause at least one problem. As Don Gause and Gerald Weinberg point out, each solution is the source of the next problem. It is very likely that you are only working on a few links in an entire chain of problems. The scope of your problem must be chosen with great care. One of the hardest things about solving a problem is knowing that it even exists.
Most problems are hidden problems.
In usability testing, a core goal is to discover problems so that they can be corrected. If you are a designer or developer, you should assume that you have done a good job. However, you must also assume that you have created more problems with your creation. Your solution is a problem. If you have these thoughts then it will be easier to know that problems exist and you can hunt them down.