Take the tour ×  What is an appropriate proverb or expression
that means one has:    1. Taken on too many tasks   2. Set out
to do something that one isn't qualified to do and hence
probably will fail   3. Set out to do something that probably is
impossible to begin with share|improve this question add comment
6 Answers  up vote 15 down vote accepted  For doing something
that is too hard, or doing too much of it at one time, I'd say
you could go with  Biting off more than he/she can chew  which
usually implies "taking on too much/too may tasks", but I think
it's fair to stretch it to "taking on a task that's too hard for
you". This is, to me, the most obvious idiom for this, but it's
fairly cliche.  You could also use  Getting in over his/her head
(as in, the water is too deep)  which implies swimming somewhere
where your feet can't reach the bottom, and yet you're not a
strong enough swimmer to handle it. You can also use  He's out
of his depth/He's in too deep  which is the same metaphor.
Neither of these