[EE] to be lost in

1. to be lost in
Eng: Be or become deeply absorbed in (something): he had been lost in thought
Vie: đắm chìm trong

E.g: he had been lost in thought - đắm chìm trong suy nghĩ
her charm was lost on me - tôi ngập chìm trong sức hấp dẫn của cô ta

[EE] in essence

1. essence <noun> /ˈɛs(ə)ns/
eng: The intrinsic nature or indispensable quality of something, especially something abstract, which determines its character
Vie: tính chất, bản chất

in essence:  Basically and without regard for peripheral details; fundamentally
Vie: về bản chất  

e.g:
- in detail the class system is complex but in essence it is simple
- in essence, the maximum of a list is the max of the first element and the maximum of the tail.