'Selfish' is an adjective, and an adjective can't take an action in English. So we need to turn it into a noun. The noun form is 'Selfishness'. I am assuming you are talking specifically about yourself, and not about people in general, so we would probably then say: "Selfishness could narrow down my options for success". We probably wouldn't use 'paths' here, though we would understand what you were saying. We use 'could' because we're talking about a possible future, you're guessing what it *could* look like *if* you were to be selfish. If you're talking generally about people, then we would say: "Selfishness can narrow down your options for success". Here, we're talking about a general principle in life (not a guess about a possible future), so we use 'can'.

I think what you mean is: "Being selfish can narrow down my paths to success." Other than that it's a perfect sentence! :)

You just need to change the adjective at the beginning to a noun and it is fine. 'Selfishness can narrow down the paths to success.' Hope this helps Bob