i should shouldnt i?

sometimes, when we can, we don't, when we want to, we don't, why?
Then when we want to,we can't, when we need to, we cant,why?

when we do, we don't need to,when we do, we shouldn't,why?
when we should, do we?, when we should, can we?, why?

sometimes, when we know, we don't, when we know, we don't want to know, why?
Then when we dont know, we want to, when we don't know, we need to,why?

I can't seem to answer these, anyone else know ?