Sherlock Holmes's personality swings between two sort of poles, as it were. For some periods he seems to be very lazy. He spends his time sitting down reading or even doing nothing. Then when he's inspired by a case, he snaps into action and that's when all his amazing skills of observation really become fine-tuned for the crime at hand. In fact, this is a very curious thing about Sherlock Holmes - maybe with a modern analysis, we might say that he has sort of bipolar disorder like that.