What is principal reasons in delaying of construction projects?

Change Order Delays

Subcontractor Delays

Shipping and Supply Delays

Climate Delays

Client-End Delays

when there is no planing or no qualified project manager

Low skill Labour and non availability of material.

Thanks for invitation 

I agreed to my colleagues and see that there are2 important issues cause delaying a project performance 

(1) Weekness of effective time management and (2)  Do not setting and meeting project deadlines