It's pretty simple rules, I don't think here needs any detailed explanation at all. We should invest only what we can afford the loss.
I only apply this rule to trading, not investing. I have almost all my money in bitcoin and I convert some to stable coins sometimes and back to bitcoin. Is this risky? I think it is worth going for than holding fiat.
But the rules applies to altcoins because some altcoins are just shitcoins and a good one just like how Luna was before it become a shitcoin, we can say altcoins is like you are gambling so should treated that way. There is still nothing bad to invest 10% of my bitcoin on altcoins, out of 10% taken, some should be profitable, but this will be after a significant bear market which I am still expecting. After bull market, converting it from altcoin to bitcoin is not bad because altcoin falls significantly than bitcoin.
Do not invest in pump and dump shit coins
To be serious about this, nobody expected Luna to be a pump and dump coin. I hope people should be wiser by this time not to invest on altcoins unless they see it as gambling and be treated as gambling.