Civil services exam tests the analytical and comprehending skills of a candidate. Exam is unique in testing the candidates ability to comprehend and analyse plethora of information and arriving at logical conclusions and judgements . It is not merely about endless data and information but about why that happens.
Institutions , simply confuse students by delivering notes etc but avoid discussing and putting emphasis on the most important ingredient i.e. writing skill.
Exam is a sum of parts and there is no particular formulae of success, what suits one may not suit the other . Developing the right mix is what preparation is all about.