There are so many factors that affects ranking. No matter how strong you have done on page optimization, in the end you have to do off-page work to rank in top 10. On page has a very important role in SEO so does off page activities. And off-page is all related to link with external sites. If you have a back-link from a high DA and a good traffic receiving website then it's beneficial for you in both the ways of getting strong back link and plus getting traffic.
In short, it is like"How good looking you are and how good looking friends you have is going to decide your social image"
There are several on-page factors that affect search engine rankings. This include:
Content of Page
Title Tag
URL
Image alt text
An Ideally Optimized Web Page
Both On-Page and Off-Page SEO techniques which affects ranking such as Content optimization, use of meta tags, alt tag, title tag, backlinks in high DA sites etc.