Going with the Rider-Waite deck, we'll relate the Eights to Strength. The Eights are like the Maiden, the will and intelligence to bring our passions to heel. By doing so, the two make the lion's energy more efficient, more powerful and lofty in purpose.
The number eight is, likewise, about limitations but also about transcending them. As with Strength, having rules allow one to achieve something higher, more divine, as wild fire banked in a fireplace creates more heat and light then if it was allowed to burn as it liked.
As Seven was the individual learning to stand his ground and prove his resourcefulness, eight is the individual bowing to limitations. Rather than defying them, he finds creative ways to get the most out of such rules. The hope being that not only will he learn from such restrictions, but that they will bring out the best in him.
Learn the Eights meaning in reversal in our reversed card meanings.