The Six restores balance; the Seven is balance challenged again, and this time no one is helping. Seven is traditionally a solitary number: not the pairs of six, not the steady doubling of eight, it falls between and won't form a tidy shape. So Sevens in every suit are one person facing something — Seven of Wands holding the high ground alone, Seven of Cups alone before seven phantoms, Seven of Swords alone carrying off the blades, Seven of Pentacles alone regarding a half-grown crop.
The Seven's core is judgement. Earlier ranks could lean on strength or on other people; the Seven leans on how clearly you see: which options are real, which threats are real, whether the thing is worth waiting on any longer.
Where you'll recognise it: stretches of holding on alone, having so many options you can't move, feeling that nobody understands your position. Running well, a Seven is strategy: you read the field, chose a path, held it. Stuck, its problem is keeping every option — the cups in the clouds on the Seven of Cups stay there forever so long as you don't choose. The Seven asks you to pick one and let the rest go.