Just like there are comfort foods, there are comfort people. The mere presence of that person will calm you down, and make you feel loved, and comforted.
Boost of self confidence
When you doubt your abilities, your best friend comes to your aid as if they know some magic words to conjure up your self-confidence and make you feel worthy and powerful.
Growth
It is that best friend who helps us get back up from distressed times and start afresh, with their funny stories, fresh ideas, and new experiences.
Honest feedback
Your bestie is usually brutally honest with you. They mean well, and that is exactly what you need to grow in life. Blind support is not as good as a genuine opinion.
Free therapist
You will find yourself running to them whenever something good or bad happens. Since they are very good listeners, they pretty much do the job of a therapist for free.