Most of the time people use this word when they should not. Most of the time people use the word cant they really should be saying "wont" or "don't want to". There are a few times where cant may be true but it may be more helpful to say "I don't know how to yet" .. At least with this last statement something can be done about it if you are willing.
Cant is such a negative, reactive word - it is so final! It does not allow for any learning or any attempts to do things another way to make something happen.
Start calling it what it really is, and speaking more helpfully to yourself.
So many people say they cant do something when they have not even given it a go! In the very saying of those words they are then stripped of the power to give it a go and learn! Next time you find yourself thinking you cant do something -- stop yourself and ask if you actually want to do it. If the answer is yes, ask yourself what is stopping you from giving it a go. Are you afraid of failing? Is it more a case of you not knowing how to do it? You may not be able to dance -- but you can go and get lessons!! Why not? It would be very rare that there would be something you cannot do if you put your mind to it.
Using the word cant is just an excuse - get rid of it and speak a different way to yourself. With the right mindset, positive attitude, and a clear vision of what you want to accomplish, the only thing that is holding you back is yourself!! How you approach an opportunity, and the result of it, is solely based on you and your attitude -- get a positive one!! You will have SO many more opportunities in life if you just get rid of that one word and replace it with the truth.