I'm reading the book Complete Spanish Grammar by Gilda Nissenberg. In page 56 is the following paragraph:
The imperfect is also used to express the past:
To indicate a mental state, a mental action, or a state of indefinite duration with verbs such as sentir, creer, conocer, pensar, querer and saber. Mental states are considered ongoing conditions
- Él pensaba en mí.
- Nos conocíamos desde que éramos pequeños.
- Le gustaba caminar por las calles.
It seems that the implication of this paragraph is that the words listed above (sentir, creer, conocer, pensar, querer and saber) are almost never used in preterit tense. Is that true?