Lok Sabha Speaker Sumitra Mahajan on Sunday expressed doubts over the effectiveness of offering reservation in education and jobs for an indefinite period to bring prosperity to the country. "The idea of Ambedkarji was to bring social harmony by introducing reservation for 10 years. But what we do is to extend the reservation every 10 years. There is a shortcoming," Mahajan said on the concluding day of a three-day event in Ranchi.