I wrote an answer to a similar question earlier. It is reproduced here:

Why will selectors not select the best talent? Since there is no logical answer to this question, the question is obviously baseless.

You may have seen some examples of bright students who lacked all round development being rejected by SSB. This is done because they do not meet the requirements of Defence Services.

Defence Services need the best students. If you are one you will be selected. You will not be selected despite high IQ if you are:

• Physically unfit.
• Show potential to create social problems in a team.
• Lack will-power, determination, mental stamina and courage.

Rejection of people like Amitabh Bachchan, Shahrukh Khan & late President, APJ Abdul Kalam raises questions about the validity of the SSB process. I have answered the major issues in point form:

• SSB is a scientific process, but applied by humans (who can err) and thus utilizing the testing techniques is an art. It is prone to mistakes, as much as qualified doctors can err in diagnosis.
• The famous persons, when they faced SSB, may not have attained the degree of competence which they attained later in their lives.
• The SSB process has to find a person adequate in all round dimensions. There is no provision of shifting marks of one quality (OLQ) to cover up the deficiency of another OLQ. For example a brilliant person who has some social adjustment issue will not be given the benefit of doubt in his weakness & thus not be cleared.

I request all aspirants to have faith in the SSB process. It is not a foolproof system but is highly reliable. Hence it is greatly respected in the country. Assessed records ( Confidential) would be kept of these illustrious people with the Defence Institute of Psychological Research (DIPR) giving clear reasons as to why they were found unsuitable to be selected!