I once read that "the one who follows the crowd will usually get no further than the crowd; the one who walks alone, is likely to find himself in places no one has ever been". I agree, and believe that although travelling alone can seem scary, it will be one of the most rewarding decisions you will ever make.
Yes, you could travel with a friend that you believe will have exactly the same ideas and expectations as you, but you will not always want the same thing...
When you travel solo, you make your own plans: you choose when to wake up, where to go and what to do. You will only do what you want, and you do not need to run your decision through anyone else. This will give you a less stressful experience and more time to enjoy the city you are visiting. And in the case you suddenly decide you do not actually want stick to your scheduled itinerary? You can just do so. There is no one to disagree or disappoint, allowing you all the flexibility to proceed exactly how you want. On top of all of this, saving money is also a big plus! When you are by yourself, it is easier to be stricter on the amount you spend, mainly regarding where and what to eat and drink. This means you can save up for more amazing experiences.
And if you feel lonely? You won't.
Travelling alone allows you to interact with people - both locals and other tourists. Hostels are a great place to meet fellow travellers, most who are also travelling solo. If you do happen to be visiting the exact same attraction the following day, then you will have some company and a distraction from being on your own. Chances are, other people you meet travelling alone are going to be incredibly interesting, and have fascinating stories about their own solo adventures to share.
Travelling alone will make you grow: you learn the importance of relying on yourself, as that is the only certainty you have.
You will learn how to take decisions and trust your choices, you will show yourself how much courage you actually have to overcome challenges and face insecurities, which will make you braver, wiser and much more confident in yourself. Still, in difficult occasions, you might also learn how unexpectedly nice some strangers can be.
From taking time to help you with directions but then deciding it is too confusing and actually walk you to the place you needed to go, to encountering an amazing bus driver that can see how tired you are so drops you off exactly where you needed to be dropped off: you will be pleasently surprised and you will realise there are some great people in the world!
After your adventure, you will come back relaxed, from a drama free holiday... You will reflect on the experience, realise how capable you really are, and you will be proud of yourself.
You will also be more open-minded, willing to meet new people and you will find yourself interested in hearing more about their culture. Finally, it is also likely that you have made at least one friend, hopefully one that lives in a foreign country and says you are always welcomed if you go visit his/her city!