Any mistake in Bitcoin, the consequence is that the money will be lost forever because there is no "forgot password" then reset via email. Bitcoin's history is filled with billions of dollars worth of other people's mistakes, such as the mistakes made by those who stored Bitcoin on the Mt. Gox exchange. This is where the principle of "not your keys, not your coins" applies. Exchanges are more precisely places for trading, not vaults for long-term storage. Every mistake that others have ever made, such as losing their Seed Phrase, getting caught in a scam scheme and wallet address network errors that resulted in the loss of millions of dollars are free lessons for us. Mistakes in the Bitcoin world in general are inevitable and the greatest wisdom is to learn from the experiences of others to avoid the same pitfalls.
People should not keeping their coin at the exchanges since that place is not a storage for the coins. People can trade and increasing their coin amounts but they should send their profits to their own wallet. Keeping their coins at exchanges is not a good decision, no guarantee the exchanges will online forever. If they can aware this and securing their coin at their own wallet, nothing to worry and they will not make a mistake with their Bitcoin investment. We have many lessons so we should always be careful and learning from others is necessary so we don't have making a mistake like them.