Many aspects of good fit are personal and subjective. Each person who wears the garment has a preferred way their clothes fit them due to their own style, body, and comfort. Each person also has a slightly different body that is unique from everyone else’s.
The designer’s vision for the style is also a subjective part of fit. The designer knows what look and silhouette they are going for as well as the type of fit they want to achieve within their brand. Every designer and brand is different and there is no right or wrong here. It is entirely up to the designer to choose how the aesthetic of the fit.
While personal preference and designer’s vision for fit are subjective, there are parts of fit that I do think are objective. Mainly the functional aspects of fit. For example, if the design is supposed to have a long sleeve, but the sleeve is several inches above the wrist, the fit is objectively bad. Similarly, if the design includes a bust dart, the dart point should point towards the apex of the bust. If it is pointing above or below the bust line, the fit objectively needs to be adjusted.
This is part of why I map design details to the body (if you missed that email, you can catch up here). If I know where each detail and seam are supposed to fall on the body, I can objectively check the fit of the sample.
I also want to understand the designer’s vision and their customer’s fit preferences. This helps both me and the designer make more objective decisions about even the more subjective aspects of fit. The fit might not be objectively right or wrong in general, but it may be objectively right or wrong for the design, goal, or target customer.