The simplest successful journey
For an online order, the happy path might be: choose a product, enter an address, pay, and receive a confirmation. A user flow can draw that route so everyone agrees on the expected result.
Real journeys have detours
Cards can be declined, addresses can be incomplete, and people can leave halfway through. Teams often describe the happy path first, then add these other routes to their acceptance criteria and tests. A happy path test alone does not show that the product handles problems well.