Although the opening moves in chess might have had a little impact on how the game is going to progress, the middle games are equally important as well. This is the period where players try to utilize their powers to the maximum. They try to bring out all their powers, the knights, bishops, rooks and ofcourse their ultimate weapon - Queen. Good players try to depend on all the powers rather on concentrating on one singe piece thus ensuring they cover most part of the board. Sacrifices are made during this phase of the game. The core purpose of making a sacrifice will be to gain a better position/mobility etc., Middle games often tells how competent you are on the board.
Similar way during our second phase in life we tend to utilize our full potential, using all our possible powers may it be money, hard work, commitment or whatever it is we have. This is a period where risks/sacrifices will be made in an attempt to attain better position later in life. If you mess up in this phase, its game over!