After all gives the idea that one thing was expected, but the opposite happened. It means 'Although we expected something different'.
I'm sorry. I thought I could come and see you this evening, but I'm not free after all I expected to fail the exam, but I passed after all Position: usually at the end of the clause.
We can also use after all to mean 'We mustn't forget that ... ' It is used to introduce a good reason or an important argument which people seem to have forgotten.
It's not surprising you're hungry. After all, you didn't have breakfast. I think we should go and see Granny. After all she only lives ten miles away, and we haven't seen her for ages. Position: usually at the beginning of the clause.