Chess is a tough old game. You need to plan ahead as well as managing short-term tactical shots. The average length of a game of chess in terms of moves might be 40-50 moves, but many games end decisively in less than 25 (known as miniatures) while others go on and on for over 100 moves in some cases. Short games that end decisively tend to involve opening mistakes or tactical oversights.
It is therefore essential to spend some time on openings and tactics training. The problem comes when players only do opening and tactics, and neglect development of their strategic and positional understanding of chess and endgame training. Of course, it is far easier to ‘do’ openings and tactics training because there are books and software galore to support players with that. When it comes to positional understanding, middle game training and endgame training, not only is this harder to do on your own, it is also less clear which resources are best to suit your level. Chess coaches can help you identify your development needs to put you on the right path to improvement, with the right resources.
Here is a short and sharp game played a few years ago where Black (who shall remain anonymous) goes wrong in the opening and doesn’t make it much further. It is not a good idea to play the Sicilian Defence unless you are prepared to learn some opening theory and have a keen tactical eye. Otherwise the game can be practically over after just 1-2 inaccurate moves.