Mercury square Lilith (orb 1.9°) creates concrete friction between the two planets. The orb is very tight; this describes a stable character pattern more than a passing reaction.
Here, Mercury in Taurus in House 9 brings intellect, language, thought, and technique into House 9 (vision, belief, study, and wider horizons), with Taurus style (nature, good food, physical sensuality, roots, resources, and perseverance); Lilith in Leo in House 12 brings pure ideal, absolute demand, fascination, and refusal of compromise into House 12 (retreat, contemplation, long time, and possible confinement), with Leo style (presence, pride, creation, and the wish to be seen).
Concrete friction: this aspect creates tension between thought, speech, obsession, purity demand, and refusal to let go. Visible angle: Mercury near the Midheaven (orb 1.4°) touches an angle; this aspect is easier to notice through social role, reputation, career, and public image. House 9 (vision, belief, study, and wider horizons) is in friction with House 12 (retreat, contemplation, long time, and possible confinement); this can create blockage, inhibition, overreaction, or repeated conflict between the two fields.