The greater part of progress is the desire to progress

On the Supreme Good, Letter LXXI by Seneca

That which is short of perfection must necessarily be unsteady, at one time progressing, at another slipping or growing faint; and it will surely slip back unless it keeps struggling ahead; for if a man slackens at all in zeal and faithful application, he must retrograde. No one can resume his progress at the point where he left off. Therefore let us press on and persevere. There remains much more of the road than we have put behind us; but the greater part of progress is the desire to progress.