I want to know the main reason that makes a project failed and what makes a project to succeed too. I am waiting for your guidance please.

Lack of connectivity in team members is also one of the reason of project failure. Other reasons are poor planning and unidentified risks.

Projects fail because the team/manager fails to identify requirements, fails to create deliverables around those requirements, and fails to utilize that various PM tools and knowledge areas to answer to both requirements and deliverables.

In regards to knowledge areas (risk, cost, time, scope, communication, stakeholders, quality, etc...) a lack of 1 of these might not be a death sentence, but it certainly hampers the project and makes it harder to reach deliverable acceptance.

If I had to rank my own list of why projects fail, I'd quickly highlight lack of communication, lack of proper scope identification, lack of quality standards to catch issues with acceptance, and lack of prioritization. I believe many projects can get by without an official WBS, especially in an agile environment, but the others included above are musts.