A common "mistake" that I see that many people do when they paint eyeliner, is that they are not accurate enough in the outer corner of the eye.
You often work on getting a perfect, sharp and even line along the lash line, but then when you have drawn along the entire eye, you still just look straight ahead in the mirror - and do not see exactly what it looks like from the sides.
It is easy to happen that, right at the outer edge, there is a small gap between the lashes and the eyeliner that you have not filled in, because the eye often slopes down a little just at the outer edges so the lash line is often a little further down than you "imagine" ”.
Close your eyes and turn your head slightly in front of the mirror and you will see if there is anything you have missed!
Hug!
English 
Swedish 
Spanish