There are very few who are lucky to qualify the Civil Services Exams in their first attempt. Even if they qualify they may not get the service of their choice and may like to attempt again to improve their ranking in the service allotment. So it is wiser to be mentally prepared for making several attempts for Civil Service exams.
A candidate who is appointed to the Indian Administrative Service or the Indian Foreign Service on the results of an earlier examination and continues to be a member of that service will not be eligible to compete at this examination. In case such a candidate is appointed to the IAS/IFS after the Preliminary Examination of Civil Services Examination, 2018 is over and he/she continues to be a member of that service, he/she shall not be eligible to appear in the Civil Services (Main) Examination, 2018 notwithstanding his/her having qualified in the Preliminary Examination, 2016.
Also provided that if such a candidate is appointed to IAS/IFS after the commencement of the Civil Services (Main) Examination, 2018 but before the result thereof and continues to be a member of that service, he/she shall not be considered for appointment to any service/post on the basis of the result of this examination viz. Civil Services Examination, 2018.More on IAS Examinations