No matter how informed or an expert you are, you could also be vulnerable, if not from your end, it could be from the device side or the manufacturers. That is why I say that since you are online, you are not 100% safe. Most experts know about not holding huge amount online, but they ignore it because of convenience or laziness. This industry is a respecter of no man.
_act- please correct your quote so that it can be clickable.
Exactly, no one is an expert in this journey of crypto, no matter how careful one is, one will one way or the way will always make mistakes that give them another experience or teach them more about crypto and this will make them to strategize their plans.
It is the realisation that things can go wrong that makes an investor work towards not leaving a major part of his holding in an exchange so as to reduce the extent of exposure to potential hack. Like the OP said, things can go wrong and the system you so much trust can get attacked which endangeres your asset in the process. To avoid that, it's only best that you have just a small percentage of your asset in an exchange that's if there's a need to while you keep the rest offline. Any activity that you know engaging in will potentially cause arm to your asset should be avoided and on your part, you've got to set measures in place that helps keep your asset always safe and secured.
There are so much issues that can happen to your device that can endanger your asset which ranges from hacks to theft and the possibility of your device even crashing.