Why is the Wedding Ring worn on the 4th Finger?

Ever wonder why do we wear our wedding rings on our 4th finger?
Why not any other finger?
And why does it have to be the 4th finger on the left hand?
Why not the right hand?

Someone once told me that there is a vein in the 4th finger on our left hand that leads to the heart, thus the wedding ring is worn on the 4th finger on our left hand because our spouse is the one who won our heart over. So much so that we chose to take the vow to stay with him/her for the rest of our lives.

However, I came across this video and found its explanation really impressive.

I tried!

Really INseparable!!!!