top 10 most common reasons for package failures

what kind of package?  what application?  we need more information to respond properly.

Your question would have been more appropriate if it was asking about Best practices to handle most commonly faced issues..
Please find below few best practices while using SSIS packages and the ways to handle it out here..
https://www.mssqltips.com/sql-server-tip-category/123/integration-services-best-practices/

Knee-jerk answers..

• Connection driver issues, especially Excel 32-bit to 64-bit.

• The source file is not the same schema as what is defined, throwing a mapping error.  HOLY GOD especially with xml files.

• There is logic/new values in the source file that the SSIS package wasn't designed to handle.

• A duplicate file was received as the source, and the SSIS package wasn't designed to detect and not process it.

• In Data Warehouse loads PK-FK relationships that the incoming source files(s) don't handle, and the SSIS package isn't robust enough to detect and handle them.

• The sum of all SSIS knowledge of the previous developer can be written on the back of a matchbook cover, in large letters, with a grease pencil.

Will think of more later.

thanks Jim - can't thank you enough --- great communicator and sense of humor ... appreciate that