The answer is: Not anchoring properly.
|Eight Archers, One Anchor Spot|
Anchor Point - The point on your face (usually on your face) that you are pulling back to when preparing to shoot. It is usually a very specific spot and you want to be using the same spot - the exact same spot - every time you shoot.
Cheeking - Pulling to an anchor point on your cheek, further to the side. Using this anchor point has a disadvantage in that you cannot see straight down the length of the arrow and when shot the arrow will end up going further to the side (to the left on a right eye shooter or to the right on a left eye shooter). [See Dominant Eye for Archery.] Cheeking effectively puts the arrow on an angle going more to the left or the right and when shot the arrow will fly more in that direction.
Note - Cheeking does give the arrow more power + speed, but it comes with a loss of accuracy.
Facewalking - This refers to a person who is anchoring inconsistently on their face, meaning they are using a different anchor point each time they shoot. Facewalking will typically cause an archer's arrows to make tall lines going up and down. (This is similar to Stringwalking, which is inconsistent placement of the arrow nock on the bowstring.)
Fishhooking - Fishhooking is when an archer is pulling to North Anchor (see North Anchor below) and is pulling the corner of their mouth further back in the direction of their cheek. The end result is the same as Cheeking (see Cheeking further above).
|William Shatner using North Anchor on a Traditional Recurve|
|Arnold using South Anchor on an Olympic Recurve|
Okay, so now that those are out of the way you will probably have an idea that Cheeking, Facewalking and Fishhooking are things you want to avoid doing. If you're either a beginner or a traditionalist then you should be pulling to North Anchor. If you are getting into Olympic archery and you have a Clicker installed on your bow, then absolutely, you should be using South Anchor.
|Katniss using South Anchor, she should be using North.|
You can see this failure in films like The Hunger Games in which Katniss pulls to South Anchor when using a longbow and again later with a recurve that has no clicker on it. Having this in a film then perpetuates false information that this is a good place to be anchoring with a traditional bow - which it is not. Katniss should be using North Anchor, but the filmmakers don't know any better.
|Not Anchoring At All|
Another way of not anchoring is to be pulling back the bow, but not pulling it back all the way to your face. This is essentially a partial draw, but it is also a failure to anchor properly. You can see this as demonstrated by Marilyn Monroe in the photo below.
|Marilyn Monroe Partial Draw|
I don't like using the word "newb" because I find it is impolite and used to discriminate against people who are beginners, but I must admit it is a word I often think of when I see people pulling close to their eyeball. Calling them "Green Archers" would be more polite and a hat tip to the 1940s serial short films produced by Columbia Pictures, "The Green Archer". (Green Arrow, the DC Comics hero is loosely based off The Green Archer serial.)
So in conclusion, always anchor - and always use an anchor spot where you can get a lot more accuracy. To learn more about this topic read Instinctive Archery Vs. Anchor Points.