Why do triggers not cause a migraine every time?

I know my triggers very well now. It seems like I have a migraine attack twice a month now. I'm just wondering why the triggers don't cause a migraine every time. Because I'll have an amazing 2 weeks and forget that I should avoid the triggers then boom I'll be sick for 3 days. I'm getting a family doctor soon. I'll discuss about medication. I was on a waitlist for a long time. (Canada)

Right now i slapped a lidocaine patch on my forehead as a last resort. I can actually open my eyes and check my phone now.