Computers generate thousands and thousands of information through processing the raw data the user inputs. The human mind is not at all different from this. For a clearer view, lets take for example the process by which a search engine in the internet undergoes. In cyberspace, one can look for a particular subject without even standing up from his seat. All he has to do is open a search engine, type the subject matter he is looking for, and wait for the results to be produced by the engine. Simple and common topics like love, the Earth, McDonalds, etc. that you might key in may produce millions of results. Some are relevant and may conform to what you are really looking for, while others are insignificant and do not focus mainly on the topic that they may only mention the word once or twice.
Like computers, particularly search engines in the internet, the mind also generates thoughts and ideas this way quick and easy, provides plentiful results, yet with complications. We can never ask a search engine to list only the ones we need, the appropriate ones, and to neglect those that hardly match what we are looking for. Likewise, relevant and irrelevant thoughts will also always pop up in our minds. We can never avoid it, but we can always check them one by one and classify as to positive or negative thoughts.