Intimidating people with your eyes
When you try to make regular eye contact with people all of the sudden, your muscles probably won't be up to the task.You'll find your eyes get tired from having to actually focus on another person.All things being equal, making good eye contact is better than not doing it, but I'd hardly say it's a factor that will completely make or break your social success.If someone has many of other things going for them socially, the fact that they sometimes look away from someone while they're talking to them isn't going to be a huge deal.I think maybe not being able to see people's expressions through them is what does it!Humans are social creatures and one of the primary ways we read social cues is through facial expression.
When they speak to people they're generally looking in their direction and come across as attentive, but because they don't feel like they're constantly aware of looking other people directly in the eyes, they believe they're not doing enough.
Especially the eye(specifically because the majority of the eyes muscles reflex/contract independent of our intent, which makes it "harder to lie though the eyes".), so by blocking them we are blind(ish) to the emotional state and intent of the person with the sunglasses.
Pretty much everyone will tell you eye contact is an important aspect of communication.
If you wish your eye contact was better then by all means work on it, but don't agonize over it too much.
It can be tricky to make consistent eye contact with people when you're not used to it.
Search for intimidating people with your eyes:
Don't expect yourself to go from 0 to 100% overnight and then never go back.