I do agree it is subjective. If one is at peace and is able to sleep well while holding such a position the it is absolutely okay.
Fact that @maheshkumar made a post here despite of sitting on a good profit means that he is not very comfortable with the position (I could be wrong, if he can clarify, and will stand corrected).
If I have 37% money in one company, I will have to make sure that out of all my time spent on stock research I have spent 37% time on that company to keep a strong conviction.
As for WB quote, most people are not WB. What worked for him may not work for us.
(In 2014, I had a concentrated portfolio of 3 stocks and while I made a lot of money, I was definitely restless during that time.)