There are some people that low hanging fruits and are much more prone to change. These will be the ones who already agree with some basic aspect of the view your trying to show them. For example, say you’re trying to show people veganism is the way to go. Then you try to outreach people who agree with the pillar of the idea: needlessly exploiting animals is wrong. If the person disagrees with the cornerstone of the idea you’re trying to instill, is worthless to continue the conversation. There will be plenty more agreeable people.
Investing your time on these targets will make much easier to change the Overton window and from there, with enough activists, some sort of snowball effect should start occurring. Like the civil rights movement or the suffragists in the US.
To expand a bit on stubbornness: as I’ve said in another comment, invest your time on people who agree with the basic idea of your position but disagree with the conclusion.
When you go talk to those people, avoid telling your opinion. Use the Socratic method to make them walk step by step towards the conclusion (see this video, pay attention to how he poses open ended questions). This way, it’s the interlocutor arriving at their own conclusion instead of you pushing your ideas on them.
Keep in mind that whenever you start debating, you’ve lost the opportunity to make them see what you see. Debates are only useful if the target of your activism is someone listening to the debate.