Heart’s Law is a theory of digital asset prices by Richard Heart. It states that Bitcoin & Altcoin prices move together, because they are bonded by their liquidity pairs. This is especially true of Bitcoin (and why the crypto market moves up and down with it). This happens because most coins can be exchanged for it. Thus the more exposure a coin has in the crypto markets, the tighter it’s price ties back to Bitcoin.
Liquidity refers to the ability to quickly and cost-effectively convert assets into cash. While Bitcoin and other cryptocurrencies also trade 24 hours a day around the globe, they are far less liquid than other asset classes. This means that transacting in Bitcoin or exchanging it for cash can come with a cost and/or time delay.
Ref: https://www.investopedia.com/articles/investing/112914/liquidity-bitcoins.asp