How would someone deal with a developer who was reluctant to take testing lessons from a tester/quality person?

Great great from Simon Tomes on Quality Assistance model moment - https://www.ministryoftesting.com/moments/ama-about-transitioning-to-quality-assistance-model

I will start from a story. At my previous job I was shifting testing left. I spoke to many developers in my company about unit testing. There was one developer who told me he doesn't believe in unit testing for FE components (React). I asked why was that and he simply didn't see the benefit. I thanked him for transparency and sharing it with me as I knew exact problem I was dealing with - someone was not reluctant, but simply didn't believe. 

When a developer is reluctant to take testing lesson from a tester/quality person I'd say do not try hard to convince them at that exact moment. Try to figure out exact reason why they are reluctant. Decode what reluctant can mean. Ask questions and take their answer as valuable information. You don't need to bring them onboard right away. You might find solution elsewhere.

Back to my story. I have decided not to convince that developer at that exact time. Frankly speaking I didn't have right words at that moment and saying generic things like unit testing is great was not going to work. What I did I found someone who was willing to take tester lesson on board. There is at least ONE person in your team who is ready to take tester lesson. They are your ally. Find them, pair up with them and share your testing lessons with them. They will definitely share positive feedback either on retro or give you kudos. Eventually, positive impact spread.

Only six months later when I worked together with a few developers building up unit tests, encouraging them do it during development process, figuring out how to do component testing later my "reluctant developer" told me how unit tests/component tests saved him from bugs during FE framework migration and only then he understood what I was trying to achieve. Some developer needs to experience, feel the goodness before they believe in it. But personally I firstly find those who are willing to collaborate and build momentum.