adv.(it's) no/little/small wonder
No wonder he was a bit upset.
It's his fault, and it's understandable that they aren't happy with him.
All the windows are open, that's why it is so draughty.
adj.understandable; pardonable; can be hardly blamed
You can hardly blame him for the mistake he made; he didn't know much about the situation.
It was his first time on the stage, and no wonder he made a mistake.
It's understandable that he was frightened; after all, he is only a child.