If you say that someone has bitten more than they can chew, you mean that they are trying to do something which is too difficult for them.

For example:

He bought the old hotel but soon realized he had bitten off more than he could chew.

He tried to renovate the entire house himself, but he soon realized he had bitten off more than he could chew. 

She accepted too many projects at work, and now she’s feeling overwhelmed; I think she’s bitten off more than she can chew. 

Be careful not to bite off more than you can chew; try not to take on too many responsibilities.

With all those extra classes and a part-time job, I think he’s definitely bitten off more than he can chew.

Tradução: dar o passo maior que a perna, tentando abraçar o mundo, ter mais olhos que barriga.