Tactics take practice and experience. Either play against good opposition (and observe the tactics they use against you) or study them on your own. In time you will get better at them.
There are more reasons (which I'm sure more people will explain), but one of the simplest reasons is that no matter how good you are in non-tactic parts of the game (strategy, endgames, openings, etc.), it all doesn't matter if you're losing material to your opponent's tactics.
They are a required basis for improvement.
why must we STUDY tactics?


Before my 8 year break from chess, I put a lot of my study emphasis into tactics; specifically, I went through Combination Challenge a couple times, and worked through Chess Tactics for the Tournament Player and The Art of the Checkmate.
It made a big difference in my game, and not just to my rating: my style of play changed from being a fairly passive player to being an aggressive attacker. It was definitely beneficial.
When I came back to chess in June, I used Winning Chess Tactics as a refresher - but found it to be a disappointment. I needed a lot of examples, which it doesn't have, and can't recommend it.
So now I work through a new tactics book with many examples (Chess Tactics for Champions) and will follow it up with a new book on mating patterns (Capablanca: a primer of checkmate).
For most players I think studying tactics yield the fastest improvement (and lay foundation for a better understanding of positional play as well).

anything can happen on the board tactics present themselves to a situation if is possible doitto alter the the result of the game where one can finish with glory.
actually why must we learn all the names for the tactics, like skewer, x-ray, pin and ..........???
why must we READ a book that explains all the topics above ( skewer,pin....) ??? To spot tactics is actually base on visualisation, so means we can just SOLVE tactics puzzles to improve........Why must we STUDY tactics??? does it really increase our ability to spot tactics???
has anyone here read a tactics book ( e.g Winning Chess Tactics )???? Does it really help us in spotting tactics???
how the experts all increase their ability to spot tactics??? by solving tactics puzzles everyday ( e.g The Manual of Chess Combination 1,2,3 and 4 )??? actually how they SPOT a tactics???? by calculating every move, or base on pattern recognition????
I saw some ppl's tactics rating on chess.com over 2500+, and some GM's game on how they use their TACTICS. I was like...... wow!! They are monsters, how they can do it....