Tension and tenderness may appear to be opposing forces, but they both find root in the Latin tendere, meaning "to stretch." In French, "to stretch" and "tender" are the same word: "tendre," which can also mean to hold one's hand out.
Both softness and the act of offering gentle attention, and something being pulled, stretched out, becoming taut, speak to reaching out beyond oneself, to an ex-ten-sion.