The phrase "endless effort" means an unlimited or infinite amount of work, energy, or activity that is put into something. It implies a continuous and persistent attempt to achieve a goal or complete a task without any signs of stopping or giving up. The term can be used in both positive and negative contexts - for example, someone may praise another person's dedication by saying they have made an "endless effort" towards achieving something, but it could also imply that the work required to achieve a goal is overwhelming and never-ending.