Firstly I’d to say that I am sorry you feel you need to keep buying gems to keep playing when it’s ment to be fun.
But I would say this is a good indication that your literally not strong enough to win that match to begin with.
I personally never buy gems to continue a match and would rather give up. Having said that I complete and win every event on my main acc and my other acc’s just have to miss out if they can’t beat a stage.
Why spend money on this, it’s just a plain outright waste of money.
This game is designed to take time and be a totally utter grind without any gain or benefit to you in real life other than wasting/killing time.
If there is something you can’t do or achieve then just be patient and try again at a later date but spending money on it will not gain you any benefits and honestly the rewards are simply not worth spending money to complete matches.
If I may suggest to you to try changing your train of thought when it comes to winning matches and just accept your not strong enough at the time and try again later as this will not only save you money and annoy you far less but also make you a better and happier player in the long run.
My alt acc’s run with nearly no spend g at all and can complete rare and epic event, they don’t have enough 5 stars to complete. My trophies are at around 2200 cups and that’s without even doing raids as I’m over wasting my time on them but it at least gives an indication of what I have achieved with hardly any spending and never ever waste gems on trying to complete a match, that just silly in my eyes.
Have fun m8