If I'm reading a script, and I'm not buying it, I need to be...

If I'm reading a script, and I'm not buying it, I need to be able to relate to the character on some level, and they need to have more than one dimension. I need to have an idea of what this guy's thinking about when he's taking a shower not on camera. And if I can't picture him taking a shower and getting dressed, then he's not a real person.