I thought it was only me; I find using the same shampoo over and over, no matter how good it is, make my hair lifeless.
I read somewhere from some hairdresser site that the hair gets used to the shampoo and once this happens, the hair would not be responding to the bounce and shine that shampoos are supposed to provide.
I myself have a stock of different shampoos which I alternate using.
There are plenty of celebrities who think that washing and shampooing hair is over-rated. I think I once read somewhere that Nigella Lawson only washes her hair twice a week.
The young actress, Shailene Woodley said in an interview that she only shampoos her hair once a month. She likes her hair oily.