The thing is that every individual or investors has there own perspective on Bitcoin, hence they advised based on there view, however in my own perspective the reason why most people advise not to sell is that they focus on the long term holding so any Bitcoin price increment does not move them to sell there Bitcoin because they believe that the price of Bitcoin in the future will surely be very higher than what the price could be now and perhaps I agree on that because Bitcoin is a very potential coin and if the price was able to go this far on this number of years you could imagine what the future will be for Bitcoin.

Also I think the main reason why some persons would also say don't buy could be those that focus more on short term holding or trading and we all know that trading is mostly buying at low and selling at higher price, so perhaps considering the fact that Bitcoin price has beginning to retrace back they became confused weather the price will continue rising or decline so perhaps at the moment the will become scared of buying.