Trophies are a Reward in Gems of War. Getting X number of Trophies is sometimes a Task.
Completing Daily Tasks gets you other Rewards. When it shows up as a Daily Task, you need a high number of Trophies to complete it. I think it's always (at least?) 40.
(My son says he's never seen a different number for this Task. He thinks it's always 40.)
I used to just grind for Trophies because this Task gives a high number of Gems (30, IIRC). I'm always in need of more Gems. They are the only way to purchase certain categories of things in game (without spending actual money, at least, which I'm chronically short on).
But today I accidentally discovered that I don't need to grind for Trophies. There are better ways to come up with Trophies.
Yesterday, "40 Trophies" showed up on my Task list. If you start a Task and don't complete it the same day, it persists. It doesn't get replaced.
Yesterday, I got 13 of the 40 Trophies I needed. It was the only Task I failed to complete yesterday.
Today, one of my new Tasks was "Complete 8 Arena fights." Arena fights also give Trophies.
So I did my 8 Arena fights to try to multitask. I figured it probably gave one Trophy per fight and that would get me to 21 total.
But it actually put me over the amount I needed. I was startled and asked my son. He said after you win your 8 matches, you get a bunch of Trophies at one time, like 25 of them.
I'm not a huge fan of Arena fights, but I hate grinding towards goals. So I now have a means to handily come up with most of those 40 Trophies quickly, without grinding.
Sources of Trophies include:
PvP games (1-3 per fight)
Raid Boss (a Guild Event)
Invasion (a Guild Event)
This list may not be comprehensive.