It's based on evidence and support only. If you're inferencing correctly, you will only be able to come to just a few possible conclusions based on the support, and from there, you'll have to choose the most likely. For instance, in the cases above, the person staring at you angrily in the car may just be insane. You may not have done anything to anger him or her. Or, he or she could be yelling at someone in the backseat whom you missed in your first observation. The woman pushing the stroller could be wheeling around an old dog. Or, she could be pushing an empty stroller in order to throw her shopping bags in there instead of carrying them. It's up to you to determine, however, what is the most likely inference and go with it based on all the supporting details and your own logic.