Mentiras piadosas is a fascinating phrase that literally translates to "pious lies" or "merciful lies". It's the Spanish equivalent of the English idiom "white lies"—small, harmless untruths told to avoid hurting someone's feelings or, in this case, to bend the rules.
In the song, Shakira reminisces about a past love, singing, "Me enseñaste a decir mentiras piadosas para poder verte a horas no adecuadas" (You taught me to tell white lies to be able to see you at inappropriate times). This line beautifully captures the feeling of a secret, youthful romance where even learning to lie felt like a sweet conspiracy.
This song is an antología (anthology) of memories from a past relationship that completely changed the singer's world. Shakira looks back on a love that taught her everything, from the profound to the wonderfully silly. She lists all the ways this person shaped her, like how because of him she “aprendí a querer los gatos” (learned to like cats) and even “aumenté más de tres kilos / Con tus tantos dulces besos repartidos” (gained more than three kilos / with your many sweet kisses).
But there's a huge catch. This person taught her how to see the sky differently, how to tell white lies to sneak away for a secret meeting, and how to write over a hundred songs. He was her entire education in love. The central problem of the song is that for all the lessons he gave her, he “olvidaste una final instrucción” (forgot one final instruction). He never taught her how to get over him, and now she doesn't know “cómo vivir sin tu amor” (how to live without your love).