This is a psychological defence mechanism in which behaviours or feelings are justified and explained in a seemingly rational or logical manner to avoid or conceal the true explanation.
Rationalisation happens in two steps:
1) A decision, action, or judgement is made for a given reason, or no known reason at all.
2) A seemingly good or logical reason is given as an attempt to justify the act after the fact for oneself or others.
This process ranges from fully conscious to mostly unconscious. People often rationalise in research because they are asked to provide explanations for behaviour that is either irrational or habitual that they have not previously had to consider or verbally justify.