"If person X actually does Y, we can legitimately infer, “X can do Y.” But if person X does not do Y, you cannot legitimately infer that they can’t. Maybe they don’t do Y because they can’t do Y. Maybe they don’t do Y because they choose not to do Y.
What’s the real story? Figuring that out requires further investigation. Before you declare that, “X can’t do Y,” start with this simple checklist:
Step 1: See if the actor in question even tried to do Y.
Step 2: If the actor tried, examine how hard he tried.
Step 3: Look at how successful comparably-able actors are when they try their very hardest."
