Why not? Grosjean was effectively a rookie when he joined the grid this year.
…which didn’t really pan out all too well for the team.
I think all rookies should have at least one or two years in a backmarker or lower midfield team, preferably with a more experienced driver as a teammate. They learn the ropes, can show their worth and get a lesson in humility. I would even dare to say that Hamilton’s issues come from never having gone through that process, which is why he felt he needed to take a step backwards to go forward.