A man left home intending to post a letter on his way to a local pub where he'd often 'have lunch'. Having walked down the hill from where he lives for a hundred or so yards he noticed that another man, a complete stranger, was walking up the hill towards him from the opposite direction. When only a couple of yards separated them the man who'd been walking up the hill suddenly stopped, swore at himself, turned around and then started to walk back down the hill in the direction from where he'd come. It seems he'd realized he'd forgotten to bring something with him and so he'd decided to return to his house to get it.
On seeing the man stop, swear at himself, then turn and walk back down the hill to presumably get what he'd forgotten to bring with him, the man who'd been walking down the hill suddenly realized he'd also forgotten to bring with him the letter he'd intended to post on his way to the pub. So he also stopped, turned around and began walking back up the hill to his house intending to get the letter to post.
However, after walking back up the hill for about ten or so strides he changed his mind and decided not to bother with posting the letter until the following day. He stopped, turned around , and set off back down the hill towards the pub again. Meanwhile the other man had also decided not to bother to get whatever it was he'd forgotten to bring with him and was walking back up the hill towards the man who was again walking down it.
According to my brother-my brother was the man on his way to the pub-the two of them then didn't even exchange glances as they passed by each other on the hill.