It's a good question, and one that depends on the amount of background info you have on how crypto works (as a market and a technology) and where we're at right now in relation to things.
A solid example of what I'm getting at is that 2017's bull run wasn't random. It didn't just happen at that point in time, but could have happened in 2018 or could have happened in 2019.. it happened in 2017 specifically for a good reason.
Bitcoin runs on a cycle.. every 4 years since it's launch the supply gets cut in half. Ask anyone with a cursory understanding of economics what it means when the supply of an asset drops dramatically while demand either remains stable or increases => increased scarcity.
It's not based on speculation and it's not based on guess work - you can model the impact of this increase in scarcity, and we know that this will happen ever 4 years that Bitcoin is still being mined.
Bitcoin's blockchain was launched in early 2009.. 4 years later (after the first halvening) we saw two major bull runs in 2013 not long after the supply was cut in half.
The same thing then happened 4 years later - again, not because of speculation or randomness, but because of a mechanism built into the core of how Bitcoin works that cut the supply in half again in 2016.
We just had another halvening for the 3rd time.
https://imgbb.com/
So for anyone who knows this information and thinks that there's more chance that for the first time that Bitcoin won't experience a significant increase in value following this halvening than it will repeat again, the onus is on you to explain what's different about this time, and what is the empirical data you have that brings you to this conclusion? (
@Blackhat Lifter)
It's not saying that it's 100% certain, but you work on a scale of probabilities, as with everything, and the probability is stacked way in the favour of the same result (bull run) coming from the same event (halvening).
To answer your other question - yes, to date a rising tide lifts all boats. When money flows into Bitcoin during a bull run it has historically been mirrored throughout the market, and statistically altcoins have always outperformed Bitcoin.