Like many people, I missed out on the foreign holiday I'd booked. I'd also class that as something about which I would be unreasonable to say "Oh god - think how much we've lost!" Losing loved ones, homes, livelihoods - yes, tragic. Losing leisure opportunities that the majority of people in the world don't get to have anyway... not so tragic.
If your holiday was so irrelevant to you, and definitely not something to be upset over losing, why did you book it in the first place? Why didn't you give the money away to all those other people in the world who don't have such chances?
Probably because, like almost everyone, you consider your own happiness way more important than 'the majority of people in the world'. The £500 - or whatever - that you spent on a week in the sun - or wherever - would go a long way towards all those 'other people'. But you preferred to spend it on what you yourself have said is a frivolity.
People are allowed to be upset about missing out on things which are important to them. They don't need your approval. I'm willing to bet the cost of your holiday that you regularly get annoyed and upset about things which might seem trivial to others, and that you don't get go around saying 'Oh I can't be annoyed by this because millions of people are worse off'. That's not actually how people think, unless they're smugging it up on MN.