The idea that there is ONE person out there, made to be with you...
The odds of meeting them are astronomical.
What if you live your whole life without meeting them?
What if you're already in a relationship when you meet them?
There is no promise that your soul mate will be hot, gorgeous, smart, caring, and loved by everyone. What if your soul mate turns out to be evil? Stupid? Unattractive? Of an unexpected gender? What if your soul mate is 30 years younger than you? Sure, looks may be secondary to personality, but it is highly unlikely that every guy could end up with a supermodel girlfriend of their dreams. There aren't enough of those types in the world to satisfy the number of men who idealize them.
What if your soul mate dies? Are you doomed to live the rest of your life knowing that you will never again find love?
Even if you find them, it doesn't mean the relationship is guaranteed to be a success. No matter how well you mesh with a person, there will always be arguments. So what happens when you are unhappy with them? What happens if they beat you or cheat on you - which can happen in a moment of weakness even when you absolutely love a person? Do you just say "fuck it" because you have no other option but to be with them?
There is no such thing as "the one." Options exist, and you choose who you think you are compatible with. That person will likely not be the ONLY person for you. It might not even be the person you love the most in your lifetime. But the relationship has to work for you, and it has to work for them. It is dedication and cooperation, comfort and happiness. Nothing supernatural or mystical about it. That's all.