One day you realise there's someone else, or worse, more than one someone else, doing almost exactly the same thing as you want to set out to do. You had this gem of an idea, all ready to start moving on bringing it to life, and then it goes up in a puff - just like that, it's over for you. You see no point in continuing when someone else has clearly already got it covered. Down tools now before wasting any more time.
You'd be wrong.
There's no such thing as competition, only other people doing something similar. At worst, they're irrelevant. At best, they're a fellow crusader, seeking to solve the same problem as you, seeking to meet the same need in the world, which can only be a good thing.
Your work carries your own unique mark - your values, your perspective, your own stories that have helped shape you and this idea of yours. You're solving this problem your way, and while the execution might be similar, the outcome, the impact you want to have, will be very different.
Don't let a little thing like competition deter you from pursung your passion.
There's room enough for everyone.