An error anywhere during the game can be unrecoverable, that&#x27;s why it&#x27;s an error. The opening isn&#x27;t special, in fact I&#x27;m sure an error in the ending is more likely to lead to a loss.<p>Chess strength _doesn&#x27;t_ depend strongly on memorization. GMs are often content to take an equal position against IMs and then just outplay them in the rest of the game.<p>At top top level, they do spend a huge amount of time on opening research, but that is because they can. They can work full time, they know who their opponents are going to be, they have engines and seconds. You can use those resources on concrete analysis of positions that might occur, but not as easily on expanding your generic middlegame knowledge. It doesn&#x27;t apply to normal GMs.