When a user types in a search, Google typically relies on HTML elements to match the content on your site to that specific query. Without optimizing key HTML elements (title, body content, headers etc..), you won't be able to rank, it's as simple as that.
For now, the following diagram should help explain the basics of which elements need keyword research attention:
The "Perfectly" Optimized Page(for the example keyword phrase "chocolate donuts")
Page Title: Chocolate Donuts | Mary's Bakery
Meta Description: Mary's Bakery's chocolate donuts are possibly the mostdelicious, perfectly formed, flawlessly chocolately donuts ever made.
H1 Headline:Chocolate Donuts form Mary's Bakery
Image File name: Body Text________________________
cocolate-donuts.jpg chocolate donuts__ ____________________________________ donuts ____________________________________ ____________________________________ chocolate donuts ____________________________________ __________________________________________________________ donuts____ __________________________________________________________ chocolate__________________________________________________ __________________________________________________________ __________________________________________________________ chocolate donuts________________ __________________________________________________________ _____________________________chocolate __________________________________________________________ __________________________________________________________ __________________________________________________________ ________________________chocolate donuts __________________________________________________________ Page URL: http://marysbakery.com/chocolate-donuts Ultimately you want to attract visitors who are going to convert into customers, if you can identify keywords which will lead to more conversions, you are more likely to see a good ROI.
Google in particular is becoming much more advanced at predicting the intent of searchers. For example, if you search for "apple," are you looking for the fruit or the technology company? Through a lot of user testing and machine learning, Google has determined that its users are probably looking for the technology company. Hence Apple's #1 position on Google.
While you do not have much control over this, user intention should be a priority when you are choosing and filtering your keywords. You want to be targeting keywords where the intention is likely to lead to a conversion for your business.