If the op means what coinmarketcap calls 'dominance', then it's sometimes true and sometimes not true. Namely, it used to be largely true before 2019, I would say. If you take a look at the price and dominance in 2017 and 2018, you can see this clear relationship that when the dominance is growing, the price is decreasing and vice versa. However, what's been happening since April of 2019 has proven this theory wrong, because Bitcoin's dominance keeps increasing more or less, and the price was at least going up for a while along with it. You can see the charts here: https://coinmarketcap.com/charts/#dominance-percentage.