I am sure you are not a native English speaker but it will be helpful for us if you can just elaborate what you are trying to say.
Technically exchanges can't sell off the bitcoins they don't own. So I see no challenge in keeping a small percentage of my bitcoin in exchanges. It helps me to get to action quickly if I spot a market opportunity.
There are just two risks, one is the hacking and second one is the financial health of the exchange. Hacking can happen anytime but the liquidation process is lengthy. Ideally you should get enough time to withdraw your coins before an exchange goes to liquidation.
