Questions & Answers about No entiendo el sentido.
Because entender is a stem-changing verb in the present tense.
The e in the stem changes to ie in most present-tense forms:
- yo entiendo
- tú entiendes
- él/ella entiende
But not in nosotros and vosotros:
- nosotros entendemos
- vosotros entendéis
This is a very common pattern in Spanish.