I'm currently practising a lot of market sizing. I usually get the logic and can structure it correctly.
However, my result is often twice as big or twice as small due to wrong assumptions.
I know my basics (household, life expectancy for people, different products etc.) however, I still tend to make bad educated guesses regarding some assumptions.
How important is it to be within 20 percent if the structure/logic is correct and most assumptions are correct too? Will the interviewer tell me directly that one assumption is wrong and help me to correct it? If yes, will this be regarded as a weakness?
For Bain interviews: how usual is it to get random, standalone estimation questions that do not really have something to do with market sizing directly? Case in Point author states that only smaller firms tend to do that, whereas MBB ask market sizing questions within the context of a larger case.