Vigor
Vigor increases Health as Trait Points are invested. It is a direct survivability choice for players who want a larger health pool, rather than a change to damage or movement.
How it works
The Traits source says Vigor increases Health by 2.5 per Trait Point invested, with a listed maximum of 50 Health at Level 20. Trait Points can be invested to level Traits, according to the wiki overview. The source does not describe how Vigor interacts with particular armor or encounters.
When it helps
Consider Vigor when increasing your Health is the goal. If you instead want to improve healing received, compare Triage; if your priority is a specific damage type, consider a damage-focused Trait.
The tradeoff
Trait Points invested here do not increase the separate damage, movement, or healing effects described for other Traits.
Your next step
Review your current Trait allocation and decide whether additional Health addresses your immediate character-development priority.
Read the supporting references
Check the edition and source version for patch-specific details. Guide methodology.