The Wheel of Fortune
Necessity was typically his reasoning, when it came to non-intellectual pursuits. Things like eating, sleeping, shopping, and keeping up a public appearance. Not that he cared, particularly, about any of these things, but there was a certain social convention which had to be met in order to avoid complication which was not worth the trouble of being stubborn.
In this case, however, necessity was a bit different. His brother had made a social call, and Sherlock had needed an excuse not to linger, John being at work and unable to provide said excuse. Simple enough, and it wasn't a lie; he had indeed told someone he'd meet them. It just hadn't been at that particular time or place. A short distance from his home, he'd found himself a busy outdoor cafe, ordered a pastry and a coffee, and seated himself in a manner befitting a man expecting visitors. That none would come was of no consequence to him; he'd spend a solid hour or slightly more people-watching, and then head home with a dejected air. Barely even a ruse, and certainly not enough to fool his brother, but it was the gesture that was important, especially considering it worked.
