Ok ! Par moment le texte en français est un peu bizarre.

J'ai modif pour le "shouldn't" et pour les "moments of relaxation".
Récapitulatif :
INTRODUCTION
"All work no play" is an expression which/that incites us to think about working without relaxing . But is it really possible ?
DEVELOPMENT
I don't adopt this motto in my life of secondary school student because, for me, the moments of relaxation after a day of work or lessons are very important . I think that if you work constantly, your body, at one moment or another, will sink mainly in stress, which will entail afterwards an attack of nerves.
When I'll have a professional life, I'll dedicate a lot/much time to my family, my husband and my children, while going to the cinema or to the restaurant, for example, at weekends.
CONCLUSION
Every human being feels like a need of working (to eat, for pleasure), but he shouldn't neglect that behind this work, he has to make way for the moments of relaxation.