I once ran into two groups of people, a group of friends walking behind a group of strangers. I looked with no facial expression at my friends, then looked at the group in front. Then smiled a bit in the general direction of the 3+ people I knew and then walked by them. This was rude and super fail eye contact–if you are friends, you should greet each other respectively. From their perspective, they saw me staring in their direction, then away, then smiling randomly towards them without eye contact–I made none of them feel like I recognized or acknowledged them personally.
That is the power of eye contact: to let someone know that you are who they are focusing on. People will like you more if you make eye contact with them, and the interaction will feel more genuine. That’s not to say you can’t look away during a conversation, but it does mean that you should be careful about how you look away, because your body language may communicate that you are disinterested or not paying attention.