1. I left in the hands of other people 2. I failed to keep it accessible to myself
It's easy to lean too far in one or the other direction by leaving stuff on a commercial service or forgotten on a single device without backups. For most folks, paper wallet and safebox is the appropriate mix since it follows traditional physical security patterns and ensures some protection from theft or damage. A strong secondary option is to be online but obscure and not advertise where your valuable data rests - perhaps your keys exist on a backup service, but they're tucked away such that an attacker has to think to look for them, and to do some forensics to track down their location. This buys time to hear the alarm bells of "your password was reset" and rotate anything valuable out of the compromised accounts.
Under no circumstances would I keep the money within any of these dedicated services: even though I use Coinbase and exchanges, it's too easy to employ social engineering and privilege escalation to get in and take everything, so any value stored in them has be considered "hot", and I only keep the amounts I want to trade on them(which at this moment is $0).