It solely the decision of any investor to decide how much he is willing to invest in Bitcoin or any other asset. Bitcoin have high return proportional to the investors Level of Accumulation of it (stash) which is guaranteed in a long run, it simply a matter of discipline, if the investor is disciplined there is nothing that can shift his focus.
Bitcoin's price performance is not guaranteed in the long run to go up - even though many folks (including myself) invest into bitcoin based on presumptions that it is more likely than not to go up in the long run... so each of us needs to establish our position size in accordance with a variety of factors, including the factor that BTC's price is not guaranteed to go up.
Sometimes I do come across people talking vehemently about their investments being guaranteed in the long run forgetting to know that uncertainty do happen even though we are making speculations but the most reasons why we make good speculations about the asset we invested on is simply because we need to be positive and hope for the best in our investments but that shouldn't mean we should be too affirmative in our analysis and speculations because so far as bitcoin is concerned, there are factors that leads to projection of it's price, so if those factors don't appear in the actual direction then it will be difficult to maintain same irrational mindset or beliefs.