First Things First: If you're training your cat to sit, stay and fetch things at your commands, perhaps you should get a dog. If you're training your cat to adroitly perch himself over the toilet seat to do his business then you're on the wrong way too.
Cats are solitary predators and they have the nature to avoid or attack those who show hostility towards them or make them do things they do not want to. Training a cat means being able to understand its nature and help him do things that you want (but be patient it is going to take a lot of time.)
Contrary to the popular opinion, the feline companions can be taught to perform on cue. The key is to successfully discover what food treat appeals him the most and to present it immediately each time he responds to a verbal cue with the desired behavior. A successful training is accomplished through praise and food rewards.
If your question is why do cats do things they do then let me just remind you that they're cats and that you're not fortunate enough to know everything about them (even though I personally wish to know what attracts them so much in the closet and what makes them urinate exactly there!) The only things you know about cats are the things they want you to know - so stop struggling! Further in the article are the basics of cat training (believe me you'll need them).
Stop all the reprimands and punishments at once!
When you made a mistake during your childhood what did your parents do? They chose to help you learn the things you were weak at rather than punishing you, and you have to do the same with your cat. Concentrate on making your relationship fun, playful, rewarding, and interesting. Sometimes this change alone does a lot of benefit which is otherwise really difficult. Cats are known to be overly active and destructive when bored. A daily play session and relaxing massages will help him calm down. The cats that feel neglected often stop using their litter box but that can be changed if you pay a lot of attention to them. It is advisable to schedule regular sessions to give the cat undivided attention and to play games, even the litter box problem would disappear over time.
Set up your cat's environment
Cats love to live an independent life- do not expect him to greet you at the door when you come after a long day at work. Don't expect it to sit with you all the time; they are not really appreciative of these things. However, if you set up an environment for them that is more or less independent (and if your cat really thinks it gives him the personal space) then you can expect a change in the behavior really soon. For example if your cat scratches furniture at home you can make the scratching post fun. Instead of telling your cat to avoid the furniture, let he furniture itself tell the cat to stay away - create new attractive things for your cat.
Reward and treat your cat
Your cat would not learn to do things overnight; spend time with him and be patient. The best way cats learn to do things is through the use of rewards, praise and positive reinforcement. Set kitty up to succeed. When he behaves in a nice manner treat him; this will give you more opportunities to teach your cat the things you want him to learn. If he responds to you calling out his name or allows you to tie a leash when you take him for a walk you must reward him.
Cats are extremely adorable animals and the kind of nature that they possess makes them even interesting to live with. Training is cat may take more time than training a dog, but if you can be a little patient about the slow progress you will definitely see the bright side of your pet cat - the trained one.