The 4-5-1 puts one player in scoring position with five supporting players behind him. This means that there is a lot of backup if the striker gets tied up with a defender. The midfielders also span the entirety of the field, meaning that a quick pass across the field can restart the play if need be.
This is a great formation for a very strong offensive line and midfielders who are talented ball handlers, but also can view the field at a glance. The midfielders should always know where the striker is positioned.
Since there is one striker, there is a lot of pressure on this player to stand out and score goals. Midfield wingers often forget that they must play defensive positions, as well. Sometimes they can get so wrapped up on the offensive work that they leave gaps open on the two sidelines because they didn't recover and get back on defense.