Perseverance
Etymology
From Latin "perseverantia," from "perseverare" (to persist), which is "per-" (thoroughly, through) plus "severus" (strict, serious, severe) — the same "severus" behind "severe." So to persevere is, etymologically, to be thoroughly severe, to hold to a thing with unrelenting seriousness. It entered English through Old French in the fourteenth century.
noun · /pur-suh-VEER-uhns/
Steady persistence in a course of action despite difficulty, delay, or discouragement.
What it names
Use it for the virtue of continuing — keeping on over the long haul when results are slow and enthusiasm has drained away.
Example
The vaccine took twenty years of perseverance through failed trials before it worked.
Related idea
Persistence is the plain fact of continuing; perseverance adds the connotation of continuing against real resistance and hardship. Tenacity stresses the grip — an unwillingness to let go — while perseverance stresses the forward motion.