"neither can they deserve the perfect one." 'neither' is used on negative sentences. A positive sentence would be: "They can either like the perfect one or the imperfect one"

I have two objections. FIRSTLY, while fdmaxey is right in that "neither" is the negative form for "either", I think neither of them are appropriate in your sentence. To clarify, I think that both "either" and "neither" should be avoided in this case. Why? In your sentence, you use a "If something, then something else"-logic, where the second clause "they don´t deserve the perfect one" is dependant on the first clause "if they can´t accept the worst of you". The most common way to express this, is simply by using "if" and "then". Note that "then" is optional, and the sentence will sound good without it. Example: If you haven´t got a driver´s license, then you shouldn´t drive. If you haven´t got a driver´s license, you shouldn´t drive. This also works with positive/negative or positive/positive clauses: If you´re allergic, you shouldn´t get a cat. If you like chicken, you should taste this incredible turkey. "Neither" is not used in these sentences, because it implies two independant clauses. Examples: I like neither milk nor honey. (Here I´ve used the either-or/neither-nor construcion). I have two dogs. Neither of them are black. They both imply two independant clauses: I don´t like milk AND I don´t like honey. My first dog isn´t black AND my second dog isn´t black. SECONDLY, the use of "can" is not appropriate in your example. "Can" implies a possibility, or that something is feasible or acceptable. Example: I don´t need a ride to work, I can take the bus. I can fly! I can do whatever I want. SUGGESTION "If others can´t accept the worst of you, they don´t deserve the perfect one." or a bit more elegant: "Those who can´t accept another´s faults, don´t deserve the perfect love."