Water needs a complete route off the roof
Every rain, the roof concentrates water at the eaves, and the gutter system's whole job is giving that water a route: into the gutter, along its slope to an outlet, down the downspout, and away from the house. Break the route anywhere and the water finds its own way, usually over the back edge toward the fascia or straight down beside the foundation.
That's why gutter problems get diagnosed as a route, not a part. A clogged outlet, a gutter that has lost its slope, a downspout that dumps at the foundation: each is a different break with a different fix, and the fix can be as small as cleaning and re-pitching or as involved as replacing a failed run. The condition of the system decides, not a package.