I work in the banking industry so I can't just try different strings until it works. These strings might represent real money. If it can't be parsed then something is screwed up. The program is reading the wrong file, the data is corrupt but my point is, there is nothing the program can do to fix it. The program simply needs to throw or log and error and someone needs to research what happened. Here's another example:

// NewV4 returns a randomly generated UUID. func NewV4() (UUID, error) { return DefaultGenerator.NewV4() }

You want a UUID but it might give you an error. What do you do except also return an error?