People seem to think they are the only ones who suffer (except for the abstract concept of people with visible suffering, like starving children and burn victims). But the kind of problems they have, they feel all alone.
In reality, everyone has problems. We all shield ourselves and shield the public. We hide our pain, wear masks with smiles (or at least emotionless stares). We know we are in pain and we actively feel it, but we do not wear our hearts on our sleeves.
The irony is that, because we all do that, we only see people smiling and sharing the positives in their lives. And we believe what we see. Everything is golden and full of sunshine except the rainclouds over our own heads.
Everybody has problems, and we are all motivated by our problems. The issues we struggle with affect how we think, what we choose to do, what we focus our attention on. No matter how a person appears outwardly, they are dealing with their own internal problems.
When you are working on your characters, keep this in mind. If you don't know who somebody is or what they should be doing, find out what their problems are and how they deal with them. The answers will come from there.