Major

Fits when consequence matters more than size

Careful Important marks consequence but can understate the large scale implied by major.

Fits when one factor is especially necessary to an outcome

Careful Key implies centrality, not necessarily large scale or broad impact.

Fits when success or safety depends on the matter

Careful Critical overstates importance if the contribution is valuable but not decisive.

Fits when rank, influence, or prominence within a field matters

Careful Leading requires comparison with peers and misfits a large unranked event.

Fits when evidence shows a meaningful effect or importance

Careful Significant can be statistical and may refer to a small but reliable effect.

Fits when amount, size, or evidence is considerable

Careful Substantial concerns magnitude and may not mean strategically important.

Suits an amount or degree large enough to deserve notice

Careful Considerable is measured and can sound weaker than a decisive major change.

Fits when effects extend across many people, places, or later decisions

Careful Far-reaching concerns breadth of consequence, not immediate size.

Suits a development important enough to mark a turning point

Careful Landmark is celebratory and should not label every sizeable improvement.