Not all 100% of searches result in clicks. 

Google's goal is to provide the best possible user experience for searchers. As such, in recent years, they have introduced several new features that answer searchers' queries immediately. 

These new features (termed 'SERP features') display information right in the search results, so that people no longer have to click through to any websites. 

For example, anyone who is looking for the founders of Google will get their answer right away:
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The Search Volume metric is not the only thing you should look at when estimating your traffic potential. Whether people click through to any of the Top 10 results matters too. 

At Ahrefs, we process tons of clickstream data to provide you with the accurate "Clicks" metrics to show you what percentage of searches actually result in clicks. 

The Clicks column shows exactly how many times per month people tend to click any pages when googling this keyword. Some searches result in a lot of clicks, while other high search volume keywords may not bring in as much traffic from search due to the low number of clicks.

As the above example suggests, the keyword "seo" has a high search volume of 125K searches per month. Yet that volume only resulted in 59K clicks. One probable reason could be that Google already gave what people wanted instantly - and there was no need to click on the search results.

The CPS (Click per Search) shows an average number of clicks for all searches. It is basically a correlation between the Clicks metric and the Search Volume of the keyword. 

The higher the CPS (i.e people clicking on a few links to satisfy their search query) -- the more chances that you'll get some traffic even if you're not ranking #1 for that search query.