To bite off more than you can chew
El que mucho abarca, poco aprieta
You bite off more than you can chew when you attempt to accomplish a task that is more than what you can really make or when you try to perform different activities at once but it is recommendable to do one at a time.
If you get a bite of something but that is too big for your mouth to chew, you will not be able to eat it. This idea now represents to undertake a task (bite off) that is too much for you to handle well (more than you can chew.