1.Invest in what you can afford to lose: I have read this line many times inside this forum and outside this forum that are crypto related discussion and what they tell you about crypto investment is to invest with the amount you can afford to lose to avoid had I know and regrets that later.
It is good not to keep coins on exchanges becuase the user do not have the complete control over his coins. It is also good to avoid scam and also hope for the best and prepare for the worst. But if you are a bitcoin holder, buy now at $36900 is still a good price. I do not think someone should just buy an amount that he can afford to lose but should be seen as an investment, I mean to invest in bitcoin and buy more at good time. If it is other coins, then you can consider it as gambling, trading or something far more risky and use the amount of money that you can afford to lose.
During a bull run, buying Bitcoin or altcoins is of course very risky, and if you are interested in buying crypto, it would be better to use the money you are prepared to lose.
Yes, we should not put our coins on exchanges because it is potentially dangerous. Yes, if we buy BTC now, I don't think there's anything wrong with it because soon there will definitely be a BTC halving, but in my opinion, if for example we buy altcoins there's certainly no problem as long as we're ready to face the risks. However, it is best to buy BTC because BTC is currently the safest cryptocurrency.
However, buying crypto during a bull run is of course very high risk, so in my opinion, even if you buy, you must be able to analyze it technically and fundamentally, so that we know when a bear market will arrive.