I'm trying to get McCready to like me. I started a conversation with him and later during the conversation it allowed me to flirt. I saved before answering and each time I reload my attempts fail. Will it always be a failed attempt? Is the answer already predetermined? Is the rain in Spain mainly falling on the plane? Any advice helps! Hello!

No it won't always fail, its random, but modified by Charisma. The higher the Charisma the better the chance to succeed.

If you keep doing it, it should pass eventually. If you have low charisma it may take a while. I always carry a charisma boosting outfit with me though. If you throw some charisma boosting clothing on and then try it again, you'll have a much better chance of passing it.

Well if you have atleast 2 charisma and willing to sacrifice 3 perk points for Black Widow/Lady Killer it should be easier. Truth be told i don't understand the new system that well. It is as random as Skyrim's persuade/bribe/Intimidate.

In a sense it is random. Ignoring perks for a moment, basically they calculate a percent chance of success based on your charisma and the difficulty of the check, and then 'figuratively roll the dice'. If you charisma is high enough you will have a 100% chance for even the most difficult checks. If your charisma is four or less (maybe three or less, not sure) you will not have any chance for success for the most difficult checks.

Charisma 11 give 100% success. Red are hard options and light yellow is easy. You can still loose an easy dialogue with 9-10 in charisma but its unlikely. easy to find clothing who give +2, add hat, glasses and a beer and you have +5.