"A quick word about competitors: competitors are a startup ghost story. First-time founders think they are what kill 99% of startups. But 99% of startups die from suicide, not murder. Worry instead about all of your internal problems. If you fail, it will very likely be because you failed to make a great product and/or failed to make a great company."
In the words of Henry Ford: "The competitor to be feared is one who never bothers about you at all, but goes on making his own business better all the time." 
"Competition is defined in the minds of customers, and they use progress as their criterion. What do consumers consider as competition? How do you understand what customers do and don’t value in a solution?" 
That will sting. At least for a brief moment. But it will.
But the question is: should you worry about competitors? Every time we did something that didn’t work, it wasn’t because of a competing product, it was because we couldn’t successfully solve the problem or users kept solving their problem in the way they were doing it before our product showed up.
We didn’t know the customer well enough as to understand how they were solving the problem and why it was working for them.
Competitors don’t matter. It might bother you when you’re told there’s another product looking to solve the same problem, but that’s usually a good sign. It means that the problem is worth solving.
What matters is ‘what is the customer looking at as competition’.
If you’re building a guitar teaching app, you’re competing with guitar teachers, an older brother who can teach the user, guitar books and - most importantly - you’re competing against a user that is frustrated because ‘learning guitar is difficult’ and will quit.
Building something you’d use has the benefit of knowing what your competition is.
Competitors don’t matter. Competition does.