I think of marriage like a leafy plant. One partner is the leafy green shoot taking the role of absorbing sunlight; the other partner is like the root system taking in water and minerals from the soil. You both need each other to thrive. If one quits — either the roots rot or the leaves brown away — the whole plant ultimately dies.
Cacti are the most resilient and thus the most successful marriages. Strong, extensive roots sustain itself through droughts. The prickly green body keeps distractions and invaders away to ensure a faithful marriage. LoL