winning chess
U can't get to the end game with out knowing how to play a good middle game and to enter the middle game you need to have atleast some knowledge about the opening.
Idk i think the transition between phases is the most important... Like opening to middle and middle to end...
Openings isn't all but important enough to practice one or two.
If an opponent makes unlogical moves during his initial development, it's easy to say whether he or she is experienced or not. It creates an open window to take advantages of those players weaknessess.
If a weaker player has a solid opening which should be possible for at least 2 or 3 moves, I'm always cautious and taking them more seriously. Probably no quick easy wins or wins within a few moves there.
Safe opening moves (not leaving pieces hanging), development, safe king, minimum pawn moves are all you really need to know about openings.
Extensive tactical pattern recongnition will usually give you some kind of material or positional advantage eliminating the need to know alot about endgame.
But you should know the basics like using the king to help promote pawns.
Truly understanding the subtle nuances of the endgame will help guide your decision making throughout the entire game. One can decide on playing positional and tactical themes NOT only to win material (which most of us being novices seem to strive for), but to win squares to place pieces, create better pawns/kings, activate the rooks, etc. for the sole purpose of a dominant endgame. I for one realize that if I can better grasp the endgame, my entire play will jump to the next level.
There is a saying in Golf... "Drive for show, putt for dough".
Meaning big drives are fancy, but in the end it's the shortgame that will shave points off your scorecard.
Same in chess... opening theory is of course helpful, but understanding how to finish the game is going to get you farther than opening knowledge.
Too often, beginners study chess openings; however, when it comes down to the end game they have no clue. The key to winning chess are the intricies of the end game (very few beginners study). Utilizing the King as a valuable piece to develop unstoppable pawns, and stopping promotion nets is a must to improve your game. There are many excellent books on endgames. "111 Winning Endgames" Pandolfini is a great tool.