Defined basically as tenacity or strength of mind, strength of purpose, Firmitas is the ability to stay with any task until that task is completed. Firmitas denotes the ability to focus your capabilities with resolve upon a goal until completion. In order to pursue that effort, one must develop within oneself the steadfastness to see the task to its finish.
Seriousness of purpose also plays a large part. The goal must be something that the individual sees as both important to himself and a worthy goal in general. A frivolous goal does not inspire one to stay with the effort. Sufficient motivation must be generated within the individual to complete the task, perhaps because of a need, rule, or reward.
Firmitas means persistent effort with an unswerving spirit. Dedicating a regular time and place for the work, with minimal distraction in a conducive environment, improves one's odds of success. One must be dogged and indefatigable in terms of quality as well as quantity of effort.
Firmitas therefore becomes a state of mind in which one keeps one's purpose constantly and consistently in focus. Yet Firmitas connotes more than simple Industria. It stands upon a bedrock of inner strength founded ultimately upon self-knowledge. One must first know what matters to one, what deserves such dedication. Inner conflict, especially nacknowledged inner conflict, will bar success.
Therefore Firmitas implies dedication not merely to the achievement of goals, but to values and principles.

Senator Marcus Minucius-Tiberius Audens

Thus Firmitas differs from sheer bullheadedness in that one has considered and meditated upon one's fundamental premises and purposes, and found that those that survive such assessment merit the devotion of a lifetime.
This provides the foundation for all subsequent effort. Those who have never followed through with such a self-examination are in peril of getting lost on a detour that can take up a lifetime. No matter how sedulous and energetic their attention to whatever they do, it doesn't qualify as Firmitas because it stands upon shifting sand. Firmitas
requires ultimate maturity. It is Volition that doesn't demand willpower; it has become an intrinsic characteristic of its possessor and smoothly orders all choices and actions.

Venti aequi et cislunia melior.