Think about it like this:
You cut some raw chicken on a cutting board, then wipe(not wash) the cutting board and reuse it with something else. That cutting board is now likely to contaminate anything else you put on it with salmonella.
The same is true for gluten. While the effects of gluten contamination is not likely to be be fatal from one contamination, a celiac will be sick for the next week or two and causes lasting damage to the small intestine.
Celiac is not cured, but with a totally gluten free diet within approx 5 years the damage to the villi has seen to be mostly healed (depends on the individual). Each contamination sets this back. Important to note that celiacs still must not ever have gluten even after the villi have recovered.
My wife has celiac, I have a gluten sensitivity (causes migraines, brain fog, other intestinal issues). When we go out we just say we both have celiac. So many restaurants claim to be be gluten conscious but really have no idea... Sometimes it's obvious ("hey, I can see that you put croutons on this and then took them off"), often not without seeing the kitchen, though.
When we found out my wife has celiac we had to replace all of our cookware, toaster (obviously!... But didn't think about it at first), cooking utensils, pots and pans, etc.
The good news of celiac is that it is easy to treat and feel much better relatively quickly. Societal nicities like going to to a restaurant, eating at a friend's or family's house, having a drink, etc are all much more stressful, though.