As a BA, The most critical part is in gathering requirements (we should understand them very well from a Business User /stake holder point of view!!!)

Reason: There might be a chance for the whole project to go in the wrong path due to wrong understanding of the Business users/ Stake holders’ needs and the gathered requirements created for the work following that step… i.e., going from A to C instead of going from A to B.

Notes: (Business Users: are the individuals who work in organizations in different departments like Logistics, accounting, finance, Inventory) in the company who wanted the software in Place for them to work on to help the Customers.

Stake Holders: Some one who is related to the Project? 2 types of People are involved :

Direct Stake holders: business end users, customers, developers, tech team.
Indirect stake holders: management etc.,
The Project Manager responsibility (usually) identifies the stakeholders, determine their needs and expectations, and more important must manage and take their help for the project success. (You should Understand them well to provide them with right service, for the right success of the project)...

SME’s: are the Subject Matter Experts , who know about that project and have in-depth knowledge about that software application used and that particular business domain knowledge like Finance ( terms and permutations etc.,) Accounting ( Business Planning, Ledger maintaining , Forecasting ) , Mortgage ( Local banking rules, Knowledge about compliancy of applications, forms/ applications that needs the authorizations of the local Government bodies or counties, Underwriting conditions( How flexible the Loan lending organizations at the individuals credit check or History)

So, The SME’s help the Project Manager or BA to help them understand about the necessities or needs of the Business Users or Stake holders like/interests- (How the Project help save time for the transactions, or? how much secure/security is needed the application wise or profitable over long run) and SME’s explain How the Stakeholders or Business Users want the application to be or appear to be for the Customers or Business Users).