can't and careless, both are negative, it is like algebra, negative negative become positive. "You can't be too careful" Here, can't is negative, but careful is not. Thus the meaning in this sentence is negative. I think, You can't be too careless is correct, but it is not the same as You can't be too careful.

yes........but sometime when we be careless it gives us a great pleasure

Hello 阿忠 ā zhōng, You seem to ask whether this one or that is correct to use in a certain context. Both sentences can't be compared, they are quite the opposite in meaning.

The sentence is fine, assuming that you are using it in the right context.

hello a zhong... you cant be too much careless or too much carefull...you need to maintain balance!