That you can end up staying in contact with ex colleagues who you didnt get on with at work but can chat with easily on social media but sometimes you lose contact with the ones you were actually quite close to in work especially if they don't have FB or Instagram?
There was a colleague I was meant to meet with but unfortunately I fell asleep and missed her visit. I told her to come back later that week if she wanted but she just liked the message and I have not heard anything since.
My DH thinks it's crazy I stay in touch with colleagues who made my life miserable at work but not her. But in this day and age, social media is the only way of really keeping in touch with ex work colleagues.