You might not realize it, but with Google, everyone's search results are a bit different. That's because they personalize your results. They do this based on:
They began doing this in 2005, just for people with Google accounts, while logged in. In 2009 they rolled this out to everyone, including those not logged into a Google account. (They do this using browser cookies).
Google knows your location history from location tracking on your mobile phone, or by the location of the IP address from your computer. They use this information to give you results tailored to your location, such as local businesses. In Google's help pages, you can learn more about how they track your location history, and how to delete it or stop saving it. See Manage or Delete Your Location History.
Google looks at the history of your last 180 days of searches, giving those sites priority in new searches. They do this because it's likely you'll want to search again for something you've found in the past. If you go to Google's Settings, you can find the section called "search activity," and turn off or edit it, if you like.
This is the record of all pages you've visited while signed in to a Google account or using Chrome or the Google toolbar. Google also uses this to give your results influenced by that history.
What this means, and what you can do
If you want to see results that aren't personalized for you, try using a private search engine like DuckDuckGo or StartPage. These engines don't personalize results like Google does. To learn more about them, see this comparison article, DuckDuckGo or Startpage.
Sometimes personalized results can be helpful (showing you results in your own region), but other times it's not. So keep these private search engines in mind.
You can also try "verbatim" search. See below for details.
How Google Adjusts Your Search Query
Google does several things in their effort to optimize your results. When you type a search query into the box, Google does the following:
Often, this improves your results, but in some situations, it doesn't.
If you would like Google to not do those changes, you can use "Verbatim" search.
To find this option, on the results page, click Tools, then switch "all results" to "verbatim." It can be interesting to compare your verbatim results with "all results." With verbatim, all of your search terms are included, and it doesn't do any of the items listed above.