The phrase "unsuccessful effort" means that someone tried to do something, but they were not able to achieve the desired outcome or goal. Full definition
But many researchers had argued that those remains were only evidence of unsuccessful efforts at wider migration. (scientificamerican.com)
Asking for such specific feedback can help all stakeholders review how successful or unsuccessful the efforts on recruiting, on hiring, and on supporting new principals have been. (thoughtco.com)
Several unsuccessful efforts have been made recently to increase this limit. (gaveltogavel.us)