Finish-to-Start relationship is straight forward as most of the tasks fall under this category. Start-to-Start and Finish-to-Finish tasks are also relatively common. However, Start-to-Finish task is not typical. Start of the predecessor triggers the finish of the successor which is rather tricky. One example I have encountered is the start of the new shift of the security guard signal the finish shift of the current security guard. ie. if the next shift security guard didn't turn up, the first shift security guard has to continue his duty.