I like to ask them the following:

"Since #Bitcoin can be simply seen as digital gold, what chance do you give it to reach gold's $10T market cap, which would mean 1 #BTC = ~$500K?"

If their answer is, for example, 25%, then I tell them they need to continue buying #Bitcoin until the price per #BTC reaches $125K.

In terms of what percentage, it should be as part of their portfolio, it could be the same as the percentage chance they give it to reach gold's market cap.

If that's too much for them, then I recommend them to start with 1-5%, which will naturally grow, the more they learn about it.