How would you explain market cap and how it affects crypto prices to an absolute idiot who thinks every crypto under $10 will reach BTC prices?

Long story short, learnt about Ethereum week or two ago and I’ve been obsessed with it and told a friend. Friend invested and now thinks ethereum can hit the same price as Bitcoin because I told him it’s the 2nd biggest crypto with real world application( he was into doge before).

Except he doesn’t believe me when I say ETH won’t be priced as the same as BTC due to something to do with the marketcap and how it would have to get bigger. I didn’t know enough to explain it to him properly since I just have a loose understanding.

How would you explain to someone that just because it’s undervalued doesn’t mean it will hit Bitcoin prices?