If you cannot pursue your dream
Not everyone manages to get admission in their dream course or college. If you have missed out either because of low marks or non-affordability, please do not settle for a career you are not interested in. There are many alternatives, and at times either they are equally good, or will take you to your goals, but at a slightly slower pace.
For example, not getting into IIT does not mean that one should not study in so many other good engineering colleges. Getting disappointed, wasting a year, or moving on to other careers when actually you wanted to be an engineer, is not the right thing to do.
If you miss out getting into MBBS, remember that you can do BHMS (Homeopathy), BAMS (Ayurveda), BDS (Dentistry), Physiotherapy, speech and hearing pathology, medical lab technology, radiography, dialysis technology, optometry, veterinary sciences, nursing, pharmacy, etc. etc., that all take you into the field of medicine.
Those who could not make it into NDA for military service, or IAS for civil service, also have various other entry options to get into the service of their choice. There are people who have started as Airmen in the Indian Air Force, completed their BE, MBA, etc, while in service, became commissioned officers, and rose up to become Wing Commanders and Group Captains. Other than IAS, there are innumerable Central and State services that are lesser known but equally rewarding.
While it is certainly advantageous and prestigious to get into nationally renowned institutions, keep in mind that a large number of very successful people studied in ordinary colleges – but they pursued their dreams relentlessly.