He was confused at first because he heard that it was unstable and risky.
Crypto is volatile and even though Bitcoin has proved itself to continue to rise even after each dip, its price is still unstable.
You can enlighten him more by telling him that fortunately, with time, Bitcoin has less volatile price than past years and previous market cycles.

Correction drawdowns in Bull markets become smaller with time.
https://studio.glassnode.com/workbench/bf532ce2-a66b-4798-6deb-bf3ba7decc59Judging from this graph , Bitcoin investment profit is a steady process and that is why it is adviceable to invest in a long-term not short,the growth from the previous years is visible, fruitful and there have been no year it has dropped below the instead increasing, therefore to me its risk is not as compared to other crypto,since the risk are being recovered.
You are wrong about the assessment of this graph but overall it's a progressive chart, only that it is not progressive all year the way you make it look. Now, the big question is whether or not Bitcoin will continue to be progressive, I predict a rollercoaster ride for it even if it will rise over time.
Bitcoin when it was low in price and has a low market cap is different from when the price is now high with over $1.2T market capitalization. No doubt that Bitcoin will continue to attract more investors where the economics of demand and supply will continue to play out but the pace will not be about doubling, tripling etc of the current price and market capitalisation as people believe. It took Bitcoin over a decade to achieve the current market cap, do you think Bitcoin will do a miracle to at least double that high liquidity?
We should not deceive ourselves, there will be some negative surprises and disappointment for sure especially if people have too much expectation on the coin.