^^Check out the video here ^^

DW;PR
(Didn't Watch; Prefer to Read)

Ever wonder why the alt coins (any cryptocurrency that isn't Bitcoin) often seem to quickly imitate the price movements of Bitcoin? Here are a few factors to consider along with a warning at the end:

Trading pairs

BTC is the center of the crypto trading scene because it is the most commonly traded coin with alt coins
It’s also the one cryptocurrency in this space that hands-down receives the most exposure to the outside world of fiat currencies. Alt coins aren’t usually paired with USDT or fiat currencies. This explains why Bitcoin is the general trendsetter in the crypto space. It is far more likely to gain exposure to "new" money flowing into this space (even if an investor's goal is to own an alt coin, they often will filter through Bitcoin first.)

Most people trade in terms of Bitcoin, they look at what Bitcoin is doing and trade accordingly. Because most alts (alt coins) are traded against bitcoin, this explains why their price movements mirror BTC.
Additionally, most people place stop orders based in BTC, not to mention the sheer volume of trading being done with trading bots. (These bots are what I believe contribute to the immediate mirroring of BTC price.)

An additional explanation why some alts don’t commonly deviate from the price patterns of Bitcoin is evidence that these alts do not have a very strong or independent community and or use case supporting it.

Please note that this is not a sweeping statement saying that Bitcoin is the only cryptocurrency with a strong community behind it, that is far from the truth at this point in the cryptocurrency space.

Take a look at the graphs of different coins on the homepage of coin market cap, the coins that perfectly match that of bitcoin are showing strong evidence that these coins don’t have much happening in terms of new developments or advancements. If this were the case, these coins would be seeing perhaps a more positive price movement or at the very least, a different price movement than BTC.
In fact if you look at the coins that aren’t perfectly mirroring Bitcoin, it’s worth it to do some digging and find out why.

This article also attempts to explain the conditions in which alts with mirror or diverge from BTC price movements:

Regarding the actual price movements themselves:

There are a few different scenarios that happen with price movements regarding bitcoin and alt coins:

Either Bitcoin increases in price while alt coins depreciate,
this is evidence of most people selling their alt coins and moving into Bitcoin.
There’s the scenario where everything is pumping,
meaning that new money is flowing into the crypto space and a lot of cryptocurrencies are benefitting.
Or after a price pump seen with bitcoin the alts have a delayed positive price actions,
in this case this happens when people choose to take some profits seen with Bitcoin and move them into other cryptocurrencies.

One piece of valuable information to remember is that anything or anyone claiming to use “historical data” as main evidence to support their cause or viewpoint that is calling for a specific price movement can and most likely will be very mistaken.
Reason being that not only is Bitcoin and cryptocurrencies still a very new asset class, it’s does not offer very much depth in regards to historical data, at all.