Many times software delivery is late, why? Give reason.

There are many reasons for late delivery of software few of them are as follows.
 - Deadline is unrealistic and decided by someone who has less technical knowledge about project.
- Continue requirement change.
- The numbers of human resources are less that will be required to do the job.
 - Future technical difficulties are not considered.
- Requirement is not properly provided by the project manager to the team member.
- Miscommunication among project team member that results in delays.