You would like everything to fall neatly into place when you’re searching for a job or hiring an employee. If you’re the employer, you would like to be able to offer the job to your best candidate and then if they decline have a chance to offer the position to your second choice, and so on down the line.
In reality, employers and job-seekers both are often confronted with a tricky dilemma of weighing a bird in the hand against two in the bush. Maybe you’re interviewing for jobs and get an offer from your second choice while your first choice is hemming and hawing and will tell you in a week whether or not they plan to make an offer.