The idea is simple. When searching for new ideas you might want to try this approach. First pick a problem you want to think about. When you get stuck the idea is to simply change the target, change the problem to a similar one or one that you think resembles the first. After thinking about some similar problems. The answers you get when thinking about the first problem might be suitable for the similar problem. With this you get to utilize the work you put down thinking about the first problem. Then going forward with the similar problem might reveal something about the first problem.