To describe or criticize a person who is not capable of doing easy tasks but want to do a harder task, just because he sees some professional doing it??
Consider (from Wiktionary):
have eyes bigger than one's stomach 2. (idiomatic) To want more than one can handle.
- 2010, Veechi Curtis, Lynley Averis, Bookkeeping For Dummies, page 75: When choosing software, don't have eyes bigger than your stomach. Rather, stick to whatever level of software you need, and no more.
Although it might be more immediately relevant to the issue of greed, the notion of overestimating one's ability can carry over idiomatically to the situation you describe.