This weekend my dad did the bravest thing I've ever imagined a parent doing: He took my younger sister, Robyn, to the airport and kissed her goodbye, then drove off while she boarded a plane for Sierra Leone . She'll be there for 5 months, working with a migration organization . She's done so much legwork up to this point, informing us all as she goes, to reassure each of us that she'll be safe. Dad has been dreading the day for months, but when it finally came, he bravely let her fly. Robyn's only 20 -- old enough to make her own decisions, young enough to take on the world without trepidation. She's the baby in our family, and Dad has raised her on his own for the last 10 years. Their relationship is much stronger and deeper, I think, than the one my brother and I share with Dad; their battles are much more intense, of course, but their rapport is remarkable. Truth be told, I think they're best friends, which is why this had to be the most difficult thing ...