8. Letting Rose Live On Without Him
One of the biggest faults - I think - with Journey's End is that the Doctor's decision to leave his clone in Rose's universe didn't seem to weigh on him at all. He didn't seem to think about it. He didn't seem to think about himself in it at all. But he was left without Rose, and without any hope to find and live on with Rose again. The Doctor did love Rose Tyler, but he did what he could for her and then walked out of her life forever. That took enormous strength, and it must have been a terrible memory.