In this game we can see that a grandmaster is playing bad moves in the opening. And yet he is not lost anytime soon. In fact there are many situations in which he can get a worse but not dead lost position by playing ...e5 at some point. Also note the amount of time it takes for White to get his game-winning attack off.
In short, as long as you're not outright blundering in the opening (which obviously does occur at class level) you can do ok for some time.
"... Every now and then someone advances the idea that one may gain success in chess by using shortcuts. 'Chess is 99% tactics' - proclaims one expert, suggesting that strategic understanding is overrated; 'Improvement in chess is all about opening knowledge' - declares another. A third self-appointed authority asserts that a thorough knowledge of endings is the key to becoming a master; while his expert-friend is puzzled by the mere thought that a player can achieve anything at all without championing pawn structures.
To me, such statements seem futile. You can't hope to gain mastery of any subject by specializing in only parts of it. ..." - FM Amatzia Avni (2008)