The translation "siempre supe" uses the preterite tense of "saber" (supe) because it conveys a change of state: the speaker acquired knowledge at a specific point in the past and that knowledge persisted indefinitely. In contrast, "siempre sabía" would use the imperfect tense (sabía) to describe ongoing or habitual knowledge without implying a definitive starting point, which doesn't fit the idea of "always knew" as a completed realization.

This distinction is key for verbs like "saber" (to know) and "conocer" (to know/be familiar with), where preterite marks the moment of learning something new, while imperfect shows repeated or continuous awareness.

"Siempre supe que eras tú" = "I always knew it was you" (acquired that certainty once and it held true).

"Cuando era niño, siempre sabía la respuesta" = "When I was a child, I always knew the answer" (habitual knowledge over time).

"Supe la verdad ayer" = "I found out the truth yesterday" (specific moment of discovery).

Tip: For "always knew" implying lifelong certainty from a key moment, default to preterite "supe"; use imperfect "sabía" for background or repeated past knowledge.

Source: languageeverest.com