bite off more than (someone) can chew

Translations
взяться за непосильное дело
He bit off more than he could chew when he agreed to manage three projects at once.
Он взялся за непосильное дело, когда согласился управлять тремя проектами одновременно.
Definitions
To take on a task or responsibility that is too difficult or overwhelming for someone to handle; to attempt more than one is capable of managing.
Words
bite

verb
откусить
off

adverb
от
more

article or possessive pronoun
больше
than

conjunction
чем
someone

pronoun
кто-то
can

functional word
может
chew

verb
жевать